tag:theconversation.com,2011:/au/topics/gem-57603/articles
Gem – The Conversation
2023-10-24T12:22:02Z
tag:theconversation.com,2011:article/214614
2023-10-24T12:22:02Z
2023-10-24T12:22:02Z
Space rocks and asteroid dust are pricey, but these aren’t the most expensive materials used in science
<figure><img src="https://images.theconversation.com/files/552576/original/file-20231006-23-aam2il.jpg?ixlib=rb-1.1.0&rect=0%2C34%2C5751%2C3794&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Meteorites can get pricey, but they're not the most expensive material. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/FranceMeteoriteAuction/e075e1b22656489db39610bafb0682af/photo?Query=meteorites&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=341&currentItemNo=5&vs=true">AP Photo/Thibault Camus</a></span></figcaption></figure><p>After a journey of seven years and nearly 4 billion miles, <a href="https://science.nasa.gov/mission/osiris-rex">NASA’s OSIRIS-REx</a> <a href="https://www.space.com/osiris-rex-asteroid-samples-land-houston">spacecraft landed</a> gently in the Utah desert on the morning of Sept. 24, 2023, with a precious payload. <a href="https://science.nasa.gov/mission/osiris-rex">The spacecraft</a> brought back a sample from the asteroid Bennu.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artist's illustration of a gray metallic spacecraft hovering above the dark surface of an asteroid, with an arm that reaches down to the surface." src="https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/552573/original/file-20231006-27-cm9a07.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">OSIRIS-REx collected a sample from the asteroid Bennu.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/20c047ec48f74f6995ffad6b0f54422c?ext=true">NASA/Goddard Space Flight Center via AP</a></span>
</figcaption>
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<p>Roughly half a pound of material collected from the <a href="https://science.nasa.gov/solar-system/asteroids/101955-bennu/facts/">85 million-ton asteroid</a> (77.6 billion kg) will help scientists learn about the <a href="https://solarsystem.nasa.gov/missions/osiris-rex/in-depth/">formation of the solar system</a>, including whether <a href="https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/101955-bennu/in-depth/">asteroids like Bennu</a> include the chemical ingredients for life.</p>
<p>NASA’s mission was budgeted at <a href="https://www.asteroidmission.org/qa/">US$800 million</a> and will end up costing around <a href="https://www.planetary.org/space-policy/cost-of-osiris-rex">$1.16 billion</a> for <a href="https://www.nasa.gov/news-release/nasas-first-asteroid-sample-has-landed-now-secure-in-clean-room/">just under 9 ounces of sample</a> (255 g). But is this the most expensive material known? Not even close.</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">professor of astronomy</a>. I use Moon and Mars rocks in my teaching and have a modest collection of meteorites. I marvel at the fact that I can hold in my hand something that is billions of years old from billions of miles away.</p>
<h2>The cost of sample return</h2>
<p>A handful of asteroid works out to $132 million <a href="https://www.hoodmwr.com/things-that-weigh-around-1-ounce/">per ounce</a>, or $4.7 million per gram. That’s about 70,000 times the <a href="https://goldprice.org/">price of gold</a>, which has been in the range of $1,800 to $2,000 per ounce ($60 to $70 per gram) for the past few years.</p>
<p>The first extraterrestrial material returned to Earth came from the Apollo program. Between 1969 and 1972, six Apollo missions brought back 842 pounds (382 kg) of <a href="https://curator.jsc.nasa.gov/lunar/">lunar samples</a>.</p>
<p>The <a href="https://www.planetary.org/space-policy/cost-of-apollo">total price tag</a> for the Apollo program, adjusted for inflation, was $257 billion. These Moon rocks were a relative bargain at $19 million per ounce ($674 thousand per gram), and of course Apollo had additional value in demonstrating technologies for human spaceflight. </p>
<p>NASA is planning to bring samples back from Mars in the early 2030s to see if any contain traces of ancient life. The <a href="https://mars.nasa.gov/msr/">Mars Sample Return</a> mission aims to return <a href="https://www.universetoday.com/161264/we-can-only-bring-30-samples-of-mars-back-to-earth-how-do-we-decide/">30 sample tubes</a> with a <a href="https://downloads.regulations.gov/NASA-2022-0002-0002/attachment_5.pdf">total weight of a pound</a> (450 g). The <a href="https://science.nasa.gov/mission/mars-2020-perseverance">Perseverance rover</a> has already <a href="https://www.universetoday.com/160109/perseverance-is-building-up-a-big-collection-of-mars-samples/">cached 10 of these samples</a>. </p>
<p>However, <a href="https://www.science.org/content/article/mars-sample-return-got-new-price-tag-it-s-big">costs have grown</a> because the mission is complex, involving multiple robots and spacecraft. Bringing back the samples could run $11 billion, putting their cost at $690 million per ounce ($24 million per gram), five times the unit cost of the Bennu samples.</p>
<h2>Some space rocks are free</h2>
<p>Some space rocks cost nothing. Almost 50 tons of free samples from the solar system <a href="https://science.nasa.gov/solar-system/meteors-meteorites/">rain down on the Earth</a> every day. Most burn up in the atmosphere, but if they reach the ground <a href="https://www.amnh.org/explore/news-blogs/on-exhibit-posts/meteor-meteorite-asteroid">they’re called meteorites</a>, and most of those come from asteroids. </p>
<p><a href="https://www.nhm.ac.uk/discover/types-of-meteorites.html">Meteorites can get costly</a> because it can be difficult to recognize and retrieve them. Rocks all look similar unless you’re a geology expert. </p>
<p>Most meteorites are stony, <a href="https://www.britannica.com/science/chondrite">called chondrites</a>, and they can be bought online for as little as $15 per ounce (50 cents per gram). Chondrites differ from normal rocks in containing <a href="https://www.amnh.org/exhibitions/permanent/meteorites/origins-of-the-solar-system/chondrules">round grains called chondrules</a> that formed as molten droplets in space at the birth of the solar system 4.5 billion years ago.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A meteorite that looks like a long gray rock with dark gray veins running across it." src="https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=305&fit=crop&dpr=1 600w, https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=305&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=305&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=384&fit=crop&dpr=1 754w, https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=384&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/552568/original/file-20231006-19-kgbnz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=384&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A chondrite from the Viñales meteorite, which originated from the asteroid belt between Mars and Jupiter.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ordinary_chondrite_%28Vi%C3%B1ales_Meteorite%29_15.jpg">Ser Amantio di Nicolao/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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</figure>
<p><a href="https://aerolite.org/shop/iron-meteorites/">Iron meteorites</a> are distinguished by a dark crust, caused by melting of the surface as they come through the atmosphere, and an internal pattern of long metallic crystals. They cost $50 per ounce ($1.77 per gram) or even higher. <a href="https://geology.com/meteorites/value-of-meteorites.shtml">Pallasites</a> are stony-iron meteorites laced with the mineral olivine. When cut and polished, they have a translucent yellow-green color and can cost over $1,000 per ounce ($35 per gram).</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A brown-gray meteorite that's roughly circular with textured ridges" src="https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/552571/original/file-20231006-21-vjnv0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An iron meteorite.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Odessa_%28iron%29_meteorite.jpg">Llez/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>More than a few meteorites have reached us from the Moon and Mars. Close to 600 have been recognized as <a href="https://sites.wustl.edu/meteoritesite/items/lunar-meteorites/">coming from the Moon</a>, and <a href="https://www.catawiki.com/en/stories/4683-10-most-expensive-meteorites-ever-offered-up-on-earth">the largest</a>, weighing 4 pounds (1.8 kg), sold for a price that works out to be about $4,700 per ounce ($166 per gram). </p>
<p>About 175 meteorites are identified as <a href="https://www2.jpl.nasa.gov/snc/">having come from Mars</a>. <a href="https://aerolite.org/shop/mars-meteorites/">Buying one</a> would cost about $11,000 per ounce ($388 per gram). </p>
<p>Researchers can figure out <a href="https://science.nasa.gov/solar-system/meteors-meteorites/facts/">where meteorites come from</a> by using their landing trajectories to project their paths back to the asteroid belt or comparing their composition with different classes of asteroids. Experts can tell where Moon and Mars rocks come from by their geology and mineralogy.</p>
<p>The limitation of these “free” samples is that there is no way to know where on the Moon or Mars they came from, which limits their scientific usefulness. Also, they start to get contaminated as soon as they land on Earth, so it’s hard to tell if any microbes within them are extraterrestrial.</p>
<h2>Expensive elements and minerals</h2>
<p>Some elements and minerals are expensive because they’re scarce. Simple <a href="http://www.leonland.de/elements_by_price/en/list">elements in the periodic table</a> have low prices. Per ounce, carbon costs one-third of a cent, iron costs 1 cent, aluminum costs 56 cents, and even mercury is less than a dollar (per 100 grams, carbon costs $2.40, iron costs less than a cent and alumnium costs 19 cents). Silver is $14 per ounce (50 cents per gram), and gold, $1,900 per ounce ($67 per gram). </p>
<p><a href="https://alansfactoryoutlet.com/how-much-do-elements-cost-the-price-of-75-elements-per-kilogram/">Seven radioactive elements</a> are extremely rare in nature and so difficult to create in the lab that they eclipse the price of NASA’s Mars Sample Return. Polonium-209, the most expensive of these, costs $1.4 trillion per ounce ($49 billion per gram).</p>
<p>Gemstones can be expensive, too. <a href="https://www.gemsociety.org/article/emerald-jewelry-and-gemstone-information/">High-quality emeralds</a> are 10 times the <a href="https://goldprice.org/">price of gold</a>, and <a href="https://ajediam.com/diamond-prices/white-natural-diamond/">white diamonds</a> are 100 times the price of gold. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A circular white diamond sitting on a white surface." src="https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=727&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=727&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=727&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554101/original/file-20231016-15-63z3ek.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">High-quality white diamonds can cost millions of dollars.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/eeaab33d812a487ebfd2e5a76a25eb03?ext=true">AP Photo/Mary Altaffer</a></span>
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<p>Some diamonds have a boron impurity that gives them a <a href="https://www.diamonds.pro/education/blue/">vivid blue hue</a>. They’re found in only a handful of mines worldwide, and at <a href="https://www.usatoday.com/story/money/2022/04/28/worlds-largest-blue-diamond-sells/9567999002/">$550 million per ounce</a> ($19 million per gram) they rival the cost of the upcoming Mars samples – an ounce is 142 carats, but very few gems are that large. </p>
<p>The <a href="https://www.sciencealert.com/scientists-create-world-s-most-expensive-material-valued-at-145-million-per-gram">most expensive synthetic material</a> is a tiny spherical “cage” of carbon with a nitrogen atom trapped inside. The atom inside the cage is extremely stable, so can be used for timekeeping. <a href="https://arstechnica.com/science/2015/12/oxford-company-now-selling-endohedral-fullerenes-priced-at-110-million-per-gram/">Endohedral fullerenes</a> are made of carbon material that may be used to create extremely accurate atomic clocks. They can cost $4 billion per ounce ($141 million per gram).</p>
<h2>Most expensive of all</h2>
<p><a href="https://www.livescience.com/32387-what-is-antimatter.html">Antimatter</a> occurs in nature, but it’s exceptionally rare because any time an antiparticle is created it quickly annihilates with a particle and produces radiation. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/7MkfMGzMcf8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">At CERN’s ‘antimatter factory,’ scientists create antimatter in very small quantities.</span></figcaption>
</figure>
<p>The <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2010.0026">particle accelerator at CERN</a> can produces 10 million antiprotons per minute. That sounds like a lot, but <a href="https://archive.ph/6RUrA">at that rate</a> it would take billions of years and cost a billion billion (10<sup>18</sup>) dollars to generate an ounce (3.5 x 10<sup>16</sup> dollars per gram). </p>
<p><a href="https://www.newscientist.com/article/mg24232342-600-how-star-treks-warp-drives-touch-on-one-of-physics-biggest-mysteries/">Warp drives</a> as envisaged by “Star Trek,” which are powered by matter-antimatter annihilation, will have to wait.</p><img src="https://counter.theconversation.com/content/214614/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>
Some space rocks you can get for free – if you know how to identify them. Rarer materials cost more, and the asteroid sample NASA just brought back has a high price tag.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/106665
2018-12-12T11:42:31Z
2018-12-12T11:42:31Z
Diamonds are forever – whether made in a lab or mined from the earth
<figure><img src="https://images.theconversation.com/files/250100/original/file-20181211-76959-fbhgqt.jpg?ixlib=rb-1.1.0&rect=169%2C33%2C4086%2C2806&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Are you in the market for some sparkle?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/great-background-image-lots-diamonds-46190779">clearviewstock/Shutterstock.com</a></span></figcaption></figure><p>It’s diamond season. <a href="http://publications.weddingwire.com/i/953286-weddingwire-2018-newlywed-report">Almost 40 percent of American engagements</a> happen between Thanksgiving and Valentine’s Day, with Christmas the most popular day to pop the question – and hand over a sparkly piece of ice. Jewelry stores do at least <a href="https://www.census.gov/retail/index.html">double their usual monthly sales in December</a>.</p>
<p>Since at least the late 1800s, with the <a href="https://www.theatlantic.com/magazine/archive/1982/02/have-you-ever-tried-to-sell-a-diamond/304575/">discovery of huge diamond mines in South Africa</a>, people have treasured these dazzling gems. The beauty and splendor of diamonds goes well beyond the surface. Like a diamond hunter digging in an underground mine, one must look deeper to their atomic characteristics to understand what sets these stones apart – and what makes them valuable not just for romantics but also for scientists.</p>
<h2>On the atomic level</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249495/original/file-20181207-128202-bhm7sv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A literal diamond in the rough, before it’s been removed from the matrix within which it formed.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Rough_diamond.jpg">USGS</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
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<p>When mined from the earth, diamonds look like cloudy rocks before they’re cut and polished. Their chemical nature and structure were unknown for centuries. It was <a href="https://doi.org/10.1007/s10818-016-9241-8">Isaac Newton’s experiments in the 1600s</a> that first suggested diamonds are made up of the <a href="https://doi.org/10.1088/1742-6596/728/6/062004">fourth-most abundant element, carbon</a>.</p>
<p>People doubted Newton’s discovery, which is understandable considering how different diamonds look from other common forms of carbon, like the graphite in pencils or the ash left over in a wood-burning fireplace. But in 1797, English scientist Smithson Tennant <a href="https://www.jstor.org/stable/24949942">confirmed the composition of diamonds</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=447&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=447&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=447&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=562&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=562&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249496/original/file-20181207-128190-1kvd31h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=562&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Diamond and graphite are both made of carbon atoms, but organized in different structures.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Diamond_and_graphite2.jpg">Materialscientist/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>It turns out that carbon takes two common forms that have crystalline structures on the atomic level. Graphite is a repeating two-dimensional, honeycomb-like shape, with layers stacking on top of each other. Alternatively, carbon can form a repeating three-dimensional shape, a tetrahedron – and that’s your diamond. </p>
<h2>Where do they come from?</h2>
<p>There are two sources of the precious gemstone: natural mining or synthesis within a laboratory.</p>
<p><iframe id="WXvk7" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/WXvk7/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Natural diamonds are formed under intense pressure and heat in the Earth’s crust over millions of years. <a href="https://doi.org/10.1007/s10818-016-9241-8">Natural deposits have been found all over the world</a>, from Northern Canada to Western Australia, even underwater in Namibia.</p>
<p>Mines were the only source of the gemstone until 1955, when General Electric produced the first synthetic diamond using what’s called the <a href="https://www.gia.edu/gems-gemology/fall-2017-observations-hpht-grown-synthetic-diamonds">high-pressure, high-temperature process</a>. This process works by applying hundreds of thousands pounds of pressure to graphite at 2,700 degrees Fahrenheit to <a href="https://doi.org/10.1007/s10818-016-9241-8">force the carbon into the correct crystalline structure</a>. It’s sort of like an artificial version of the extreme conditions that produce diamonds deep within the earth.</p>
<p>In the 1970s, labs started to use the chemical vapor deposition method to grow diamonds at lower pressures. At the time, the HPHT technique couldn’t produce a gem-quality stone. This improved method converts a hydrocarbon gas mixture by breaking it down to its components, carbon and hydrogen molecules, with an intense heated filament or plasma and deposits it onto a substrate, ultimately forming a solid diamond. Originally, this process had a very slow growth rate, but it’s now optimized to <a href="https://doi.org/10.1557/S0883769400061480">grow quality diamonds within days</a>.</p>
<p>Together these techniques are largely responsible for human-made diamonds – upwards of <a href="https://www.statista.com/statistics/280216/global-synthetic-diamond-production/">4 billion carats worldwide annually</a>.</p>
<p>There’s a common misconception that a natural diamond must be inherently different than a synthetic diamond. To the contrary, they are chemically identical and share the same physical properties. Even the most sophisticated techniques can not detect a difference between a flawless mined diamond and a flawless human-made diamond – both are “real” diamonds. However, truly flawless diamonds of either type are extremely scarce.</p>
<h2>Assessing a diamond</h2>
<p>No matter its origin, a diamond can be assessed by the “four Cs” of cut, color, clarity and carat weight. Specialized laboratories grade each category, as created by the Gemological Institute of America.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=318&fit=crop&dpr=1 600w, https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=318&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=318&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/250102/original/file-20181211-76980-13b3err.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Diamond cutters choose the shape of the finished stone.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/twenty-one-various-diamond-shapes-cut-739328245">SPbPhoto/Shutterstock.com</a></span>
</figcaption>
</figure>
<p><a href="https://doi.org/10.1111/j.1475-3995.2005.00516.x">The cut of a diamond</a> is defined in two ways. There’s “the general shape of the cut stone,” with shapes including round brilliant (most common), oval, emerald, pear, princess, trilliant, triangle, heart and radiant. And there’s “the degree of perfection achieved by the cutting and polishing process” as rated on a scale ranging from excellent to poor. The type and quality of the cut ultimately determines the way light reflects in the stone, contributing to its “brilliance.” </p>
<p><a href="https://www.gia.edu/doc/Coloring-Grading-D-to-Z-Diamonds-at-the-GIA-Laboratory.pdf">The color of a diamond</a> is graded on a scale from “D,” being perfectly colorless, to “Z” having the most color. Originally, the color of the stone was a huge hint about how it was formed because until 2007 about <a href="https://www.gia.edu/gems-gemology/fall-2017-observations-hpht-grown-synthetic-diamonds">90 percent</a> of the high-pressure, high-temperature synthetic stones were yellow orange or yellow. Almost no stones from that process were colorless, so a colorless stone was almost certainly natural. But the HPHT growing process has greatly improved and as of 2016, <a href="https://www.gia.edu/gems-gemology/fall-2017-observations-hpht-grown-synthetic-diamonds">43 percent</a> of synthetic diamonds were colorless.</p>
<p><a href="https://www.gia.edu/gia-about/4cs-clarity">Diamond clarity</a> indicates the presence of inclusions, or tiny imperfections, in the stone. Inclusions make every diamond unique and provide strong clues to whether a diamond is natural or synthetic. The HPHT process <a href="https://www.gia.edu/gems-gemology/fall-2017-observations-hpht-grown-synthetic-diamonds">uses metal flux</a>, or a hot metal liquid, which acts as a solvent to dissolve the carbon source, graphite, to be rearranged and grown into a diamond. Diamonds grown this way can have inclusions of metals. The resulting stones may be magnetic – if a diamond reacts with a magnet, it is certainly synthetic. Additionally, most synthetic diamonds receive high clarity grades, while natural diamonds contain larger inclusions. </p>
<p>Many consumers focus on <a href="https://4cs.gia.edu/en-us/blog/gia-diamond-grading-reports-understanding-carat-weight/">carat weight</a> – that is, diamond size. The stone is weighed on a scale where one carat is 200 milligrams (0.007 ounces). Diamonds larger than four carats are almost guaranteed to be natural because that’s the limit for the size of the diamonds that the synthetic processes can grow.</p>
<p>Although the “four Cs” of diamonds ultimately define retail value, sentimental value can be even greater. Buyers must decide if a natural or synthetic stone fits the bill for them, based on factors that might include the <a href="https://www.businessinsider.com/millennials-want-cheap-ethical-diamond-engagement-rings-2018-5">ecological and ethical ramifications</a> of diamond mining as well as the lower price tag for synthetic rocks. </p>
<h2>Diamonds found beyond your ring finger</h2>
<p>Although diamonds are well known for their place in the jewelry industry, they play other valuable roles, too.</p>
<p>Their physical properties, especially hardness, are ideal for abrasive applications. Small diamonds can be found <a href="http://pdc-guru.com/uploads/2/8/7/9/2879895/daw_d-scott_history-and-impact-of-synthetic-diamond-cutters-in-og.pdf">coating cutting wheels, drill bits and grinding wheels</a>, which are used for cutting concrete or brickwork.</p>
<p>Diamonds also have certain optical properties that make them suitable for various spectroscopy techniques, or measurements involving the electromagnetic spectrum. Scientific researchers use these tests to help identify the composition of materials they’re investigating.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/249851/original/file-20181210-76977-1s1d3uc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A diamond needle is what’s in contact with the grooves on a record.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/hawkins-thiel/3235580260/">Michelle Hawkins-Thiel/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>A previously common place for diamonds was on record players, where to this day the <a href="https://patents.google.com/patent/US3902340A/en">needle that touches the record</a> can be a very small diamond sliver.</p>
<p>Whether one appreciates the aesthetic or scientific characteristics of the gem more, diamonds can dazzle.</p><img src="https://counter.theconversation.com/content/106665/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Whether forged by geological processes or laboratory techniques, diamonds are diamonds. Their unique properties mean they have applications that are not bling-related as well.
Joshua Wilhide, Manager of the Molecular Characterization and Analysis Complex, University of Maryland, Baltimore County
William LaCourse, Professor of Chemistry and Dean of the College of Natural and Mathematical Sciences, University of Maryland, Baltimore County
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/97084
2018-08-09T20:07:47Z
2018-08-09T20:07:47Z
A disappointing earring, and the world’s hottest rock: zirconia
<figure><img src="https://images.theconversation.com/files/225645/original/file-20180702-116152-d01eb5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Diamond or zirconia? Apart from the price, it can be hard to tell these two gems apart. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-beautiful-woman-wearing-vinyage-shiny-513160801">from www.shutterstock.com </a></span></figcaption></figure><p><em><strong><a href="https://theconversation.com/au/topics/my-favourite-gem-56779">My favourite gem</a></strong> is an occasional series in which we ask a scientist to share the fascinating geological and social features of a beautiful rock.</em></p>
<hr>
<p>Just last week, my partner handed me an earring that she had found in a park near her home more than seven years ago, and for which she’d had no luck finding the owner.</p>
<p>The earring had a gold setting that gripped a very large, transparent, beautifully cut gemstone. Given that I am a geologist, she asked me to check it out for her to find out more about the stone. After all, we thought, if it was a diamond, then it could fund a holiday to somewhere lovely, given its large size. Hawaii, perhaps? </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-we-value-diamond-rings-and-other-valentines-day-gifts-89056">Why we value diamond rings and other Valentine's Day gifts</a>
</strong>
</em>
</p>
<hr>
<p>Upon analysing the earring under an electron microscope, it was immediately apparent that the earring wasn’t a real diamond. It turned out to be cubic zirconia. </p>
<p>Funnily enough, zirconia is a topic very close to my heart and my professional expertise. In 2017 I wrote a <a href="https://www.sciencedirect.com/science/article/pii/S0012821X1730451X">research paper</a> on the “world’s hottest rock”, and zirconia was part of that story. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=782&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=782&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=782&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=983&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=983&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221701/original/file-20180605-175445-18iw252.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=983&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A false colour image of a grain of zircon (yellow) that has formed a rim of zirconia (multicolours) at 2,370°C when the surrounding rock melted during an ancient meteorite impact. This is the hottest known temperature to be achieved by any rock naturally at Earth’s surface.</span>
<span class="attribution"><span class="source">Nick Timms</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Crystal lattice gems</h2>
<p>Zirconia is a mineral with a crystal structure made from the elements zirconium (Zr) and oxygen (O), with the chemical formula ZrO₂. It looks quite a lot like diamond, but is only worth a fraction of the value because it is manufactured and not a rare natural gem. </p>
<p>Cubic zirconia belongs to a family of zirconia minerals, each having a different configuration of atoms that give rise to different crystal lattice structures, called polymorphs. Similarly, graphite and diamond are polymorphs of carbon – each made entirely of carbon but with different structures. </p>
<p>Like diamond, cubic zirconia is stable at very high temperatures and pressures.</p>
<p>But unlike its sparkly friend diamond, cubic zirconia isn’t stable at Earth’s surface. In fact, it has never been found in natural rocks, which is why it hasn’t been given a proper mineral name by geologists. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-a-gem-and-why-painite-from-myanmar-can-fetch-us-60-000-per-carat-97453">What is a gem? And why painite from Myanmar can fetch US$60,000 per carat</a>
</strong>
</em>
</p>
<hr>
<p>When zirconia is manufactured for making jewellery, the manufacturers use additives to stabilise it. Impurities are incorporated into the mineral and act like atomic scaffolding, holding the structure together so that it resists transforming into one of the other zirconia polymorphs. </p>
<p>If it is pure, though, it readily morphs into one of its siblings – first to a form known as tetragonal zirconia, then to baddeleyite – a polymorph of zirconia that is stable at room temperature. Every time the atoms shift to transform into a different polymorph, they leave evidence behind within the crystal. </p>
<h2>Earth’s hottest rocks</h2>
<p>So what has this got to do with the hottest rocks on Earth’s crust? </p>
<p>I am interested in finding out how Earth responds when asteroids hit it. I have studied a few of the 192 meteorite impact craters that have been discovered on Earth, including the one that was ultimately responsible for ending the existence of the dinosaurs. </p>
<p>Australia has its fair share of craters – Wolfe Creek is particularly well known, made famous by a chilling horror movie. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/target-earth-how-asteroids-made-an-impact-on-australia-92836">Target Earth: how asteroids made an impact on Australia</a>
</strong>
</em>
</p>
<hr>
<p>Canada’s ancient landscape has also accumulated many scars of bombardment. One particular ancient impact structure – Mistastin Lake in Labrador – contains the solidified remnants of a lava flow near its centre that forms huge cliffs called Discovery Hill. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=575&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=575&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=575&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=723&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=723&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229920/original/file-20180731-176708-1al832i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=723&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mistastin Lake in Canada sits in a meteorite impact crater.</span>
<span class="attribution"><span class="source">Google Maps</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The energy released by the meteorite impact was enough to melt and even vaporise the rocks at ground zero, which then cooled quickly (quenched) to form the glassy black rocks of the cliffs. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=138&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=138&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=138&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=173&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=173&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229922/original/file-20180731-176708-1ieoise.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=173&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The impact structure at Discovery Hill, Mistastin Lake – where the world’s hottest rock was found. CLICK TO VIEW.</span>
<span class="attribution"><span class="source">Mike Zanetti, Western University, Canada.</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The rocks had the texture of syrup when I examined them under the microscope, and I could easily see that only a few fragments of the most physically robust minerals had escaped being completed melted. </p>
<p>Frozen in this quenched rock soup were a few little remnant grains of the mineral zircon (with the chemical formula ZrSiO₄). The zircon must have been present in the target rocks before the catastrophic event, and had taken a “hot bath” when they became immersed in the lava. </p>
<p>However, zircon is a tough cookie and doesn’t melt when it is heated. Instead, and at high enough temperatures, it decomposes to form tiny crystals of zirconia and liquid silica. The specs of zircon in this particular rock had begun to decompose, reacting within the hot magma and had become encrusted with a beautiful rind of zirconia (the baddeleyite form).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=465&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=465&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=465&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=585&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=585&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229926/original/file-20180731-176711-1qocy3i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=585&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Rock collected from the top of Discovery Hill, on the southweastern edge of Mistastin Lake (shown in the photographs above).</span>
<span class="attribution"><span class="source">Mike Zanetti, Western University, Canada</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>My research team could read the paper trail in the baddeleyite, detecting the former presence of cubic zirconia from which the baddeleyite had transformed. This meant that this rock had once been at a blistering 2,370°C during the impact event around 38 million years ago. This is the <a href="https://www.sciencedirect.com/science/article/pii/S0012821X1730451X">hottest temperature ever recorded</a> for a rock anywhere on Earth’s surface. </p>
<p>This finding made us wonder what might Earth have gone through early in its history, when it was being bombarded frequently by similar-sized or even bigger impacts, and its surface was subject to these extreme temperatures on a regular basis.</p>
<p>There’s an amazing sense of excitement and awe from making discoveries from studying tiny mineral fragments in rocks that spark such deep thoughts about events and timescales almost beyond comprehension. Luckily, this can offset the mild feeling of disappointment after analysing a found earring. </p>
<p>Another time, Hawaii, another time! </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/life-death-and-politics-in-hawaii-125-years-of-colonial-rule-90273">Life, death and politics in Hawaii: 125 years of colonial rule</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/97084/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nick Timms does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Zirconia is a mineral with a crystal structure made from the elements zirconium and oxygen. It looks pretty like diamond, but is only worth a fraction of the value.
Nick Timms, Senior Lecturer, Curtin University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/98474
2018-08-08T20:09:10Z
2018-08-08T20:09:10Z
Sapphire secrets: they aren’t all blue, and mining them requires luck plus labour
<figure><img src="https://images.theconversation.com/files/224385/original/file-20180622-26546-1abhc5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sapphire beads in a Jaipur workshop. </span> <span class="attribution"><span class="source">Lynda Lawson </span>, <span class="license">Author provided</span></span></figcaption></figure><p><em><strong><a href="https://theconversation.com/au/topics/my-favourite-gem-56779">My favourite gem</a></strong> is an occasional series where we ask a scientist to share the fascinating geological and social features of a beautiful rock.</em></p>
<hr>
<p>I first remember seeing sapphires as a teenager in a jeweller’s shop in Silver Street in pre-Khmer Rouge Phnom Penh – the deep saturated blues of the gems from Palin on the border with Thailand were captivating. The sapphires my father bought that day are still in the family long after any trace of Silver Street has disappeared. </p>
<p>It was not until recently when I met a female sapphire miner in Madagascar that I began to appreciate the hard labour involved in the mining of these stones across Africa and Asia.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-a-gem-and-why-painite-from-myanmar-can-fetch-us-60-000-per-carat-97453">What is a gem? And why painite from Myanmar can fetch US$60,000 per carat</a>
</strong>
</em>
</p>
<hr>
<h2>Inside sapphires</h2>
<p>Sapphires are crystals of the mineral corundum, made up mostly of atoms of aluminium and oxygen in a 2 to 3 ratio (Al₂0₃). </p>
<p>The chemical bonds of aluminium and oxygen are particularly tight, making the sapphire one of the hardest minerals known – 9 out of 10 on a measure of hardness used for minerals known as <a href="https://geology.com/minerals/mohs-hardness-scale.shtml">Moh’s scale</a>. Sapphires are second to diamonds in hardness. </p>
<p>This quality makes the stone valuable for jewellery, as it keeps its shine and does not scratch. </p>
<p>The aluminium and oxygen do not reflect light, making sapphires transparent, another characteristic that is highly prized in a gemstone.</p>
<p>The tight chemical bonds of corundum also make the stones very dense and relatively heavy. This means they are not swept away during weathering, but accumulate in alluvial deposits – that is, left behind by the flow of water. As a result, sapphires can be found by miners tunnelling down to ancient riverbeds or in bends of existing river beds. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Oq-rqbkZo0s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Understanding coloured gemstones.</span></figcaption>
</figure>
<h2>Different shades of blue</h2>
<p>The colour of corundum comes not from the aluminium or the oxygen, but is due to <a href="https://www.youtube.com/watch?v=j1Y2E237ZbM">impurities and inclusions in the crystalline structure</a>. </p>
<p>The blue of sapphires is from substitution of both iron and titanium in place of some of the aluminium. The shade of blue will depend on the ratio of ferrous iron and ferric iron, with higher levels of ferrous iron producing the inky blues characteristic of Australian sapphires. </p>
<p>Corundum that is red is known as ruby – and results from the presence of chromium substituting for aluminium in the crystal structure. </p>
<p>Yellow sapphires are often caused by the presence of iron without the involvement of titanium. </p>
<p>Star sapphires – rare sapphires which reflect a star in certain light conditions – occur when fine needle-like inclusions of minerals such as rutile are aligned parallel to the six sides of the hexagonal crystal shape of a sapphire. When cut correctly, light reflects causing a six rayed star to appear. </p>
<h2>The black star of Queensland</h2>
<p><a href="https://www.sustainablegemstones.org/videos/">Sapphires and rubies</a> were created many millions of years ago through one of two geological processes: metamorphic (involving rock transformation) or magmatic (associated with volcanoes).</p>
<p>Metamorphic stones grew during ancient mountain building events such as continental collision – where heat and pressure caused the crystallisation of gem quality corundum. </p>
<p>Metamorphic sapphire and ruby deposits are among the finest in the world. Traditionally they have been found in Sri Lanka, Mogok and Kashmir and more recently in Mozambique, Tanzania and especially Madagascar. </p>
<p>Magmatic sapphires and rubies are not associated with a mountain building event but were carried to the surface in volcanic events from deep in the earth. Magmatic sapphires and rubies occur in eastern Australia, Southeast Asia, Africa, and North America. </p>
<p>Queensland has produced some of the world’s most famous sapphires: the <a href="https://jewelry-blog.internetstones.com/the-black-star-of-queensland-famous-black-sapphire-gemstone/">Black Star of Queensland</a> at 1,156 carats (uncut), is the largest black sapphire ever found.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229917/original/file-20180731-176698-x1htq7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Now about the size of a large egg, the Black Star of Queensland sapphire was once used as a doorstop.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Black_Star_of_Queensland_Star_Sapphire.jpg">Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>It was discovered on the Anakie sapphire fields in Central Queensland in 1938 by 12 year old Roy Spencer. His father used it as a door stop, until it was bought by an American collector, and cut and polished into a magnificent oval cabochon which displays a six point star. Its current value could be as much as <a href="https://www.thenaturalsapphirecompany.com/blog/the-black-star-of-queensland">US$50 million</a>. </p>
<p>Today there is a strong demand for fine quality sapphires from East Asian and European markets. Especially prized are the velvety blues of Kashmir sapphires, and the pink orange hues of the padparadscha sapphire (named after the lotus flower). </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-gold-rushes-helped-make-the-modern-world-91746">How gold rushes helped make the modern world</a>
</strong>
</em>
</p>
<hr>
<h2>The social cost of sapphires</h2>
<p>Jewellers and consumers in the West are increasingly interested in the origin of their stones and to know that <a href="https://www.vogue.com.au/fashion/accessories/how-the-jewellery-industry-is-cleaning-up-its-act/news-story/424bff47fc08bb20d7395559becbb0c6">human rights have been respected</a> in their mining and cutting. </p>
<p>Industry bodies such as <a href="https://www.responsiblejewellery.com/">The Responsible Jewellery Council</a> are seeking to create standards for coloured gemstones, which take into account the social and environmental impact of mining and the sustainability of the industry. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227558/original/file-20180713-27036-1mfy790.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A family group sieving for sapphires in South West Madagascar.</span>
<span class="attribution"><span class="source">Lynda Lawson</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p><a href="https://www.sustainablegemstones.org/">The GemHub project</a> – a collaboration between the Universities of Queensland, Delaware and Lausanne, and funded by Tiffany and Co Foundation – seeks to improve knowledge about coloured gemstones and sustainability issues linked to the mining, processing and trading of these precious resources. </p>
<p>My work with this project has taken me to the world’s gem stone hub of Jaipur to investigate the health and safety of gem cutters, particularly the risk of silicosis, an occupational lung disease caused by the <a href="https://theconversation.com/explainer-what-is-silicosis-and-why-is-this-old-lung-disease-making-a-comeback-80465">inhalation of silica</a>. </p>
<p>Today this has largely been controlled by a process of wet cutting and clean up, but the problem still remains in smaller shops among agate and quartz cutters, especially in cottage industries in Gujarat.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-silicosis-and-why-is-this-old-lung-disease-making-a-comeback-80465">Explainer: what is silicosis and why is this old lung disease making a comeback?</a>
</strong>
</em>
</p>
<hr>
<p>I have also worked with remote Madagascan communities of sapphire mining women on a basic field gemmology training course written and delivered by young Australian geologist <a href="https://www.lawsongems.com/">Charles Lawson</a>. </p>
<p>The women miners’ and traders’ negotiating skills are greatly enhanced by knowing their stones and being able to use simple tools such as tweezers and a loupe (a small magnifying glass). This has been financially empowering to the women, and they are now starting to organise their own trading and polishing shop. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227559/original/file-20180713-27039-yr4nb2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Malagasy sapphire miner learning to use loupe and tweezers to identify her stone.</span>
<span class="attribution"><span class="source">Lynda Lawson</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>However, there is still some way to go before women and men working at the very first stage of the sapphire value chain receive equitable compensation for their work in mining and trading these rare and wonderful stones. </p>
<p>The price for small rough stones can be under a dollar a carat. When cut and polished, the best of these stones can fetch up to AU$100 a carat and fine, larger stones many times that.</p><img src="https://counter.theconversation.com/content/98474/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lynda Lawson receives funding from
Tiffany and Co Foundation and
Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH (GIZ) , a German development agency</span></em></p>
Sapphires and rubies are both crystals of the mineral corundum - but with different impurities to create blue and red hues. Australian sapphires are renowned for being inky blue.
Lynda Lawson, PhD candidate , The University of Queensland
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/97453
2018-08-01T04:34:37Z
2018-08-01T04:34:37Z
What is a gem? And why painite from Myanmar can fetch US$60,000 per carat
<figure><img src="https://images.theconversation.com/files/230128/original/file-20180731-136646-k0u6lv.gif?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The first three Natural History Museum painites – including one in its natural state with rubies that had been sitting in their collection for years. It had initially been misidentified as the much less valuable tourmaline.</span> <span class="attribution"><a class="source" href="http://www.nhm.ac.uk/">© The Trustees of the Natural History Museum, London</a>, <span class="license">Author provided</span></span></figcaption></figure><p><em><strong><a href="https://theconversation.com/au/topics/my-favourite-gem-56779">My favourite gem</a></strong> is an occasional series where we ask a scientist to share the fascinating geological and social features of a beautiful rock.</em></p>
<hr>
<p>Humans have adorned themselves and their belongings with attractive stones since prehistoric times. We’ve used fossil materials such as jet and amber, colourful rocks such as lapis lazuli, and water-clear single crystals of minerals such as amethyst and golden citrine. </p>
<p>The “precious stones” diamond, ruby, sapphire and emerald are distinguished from the remaining “semiprecious stones” largely on the basis of perceived rarity in classical times.</p>
<p>But what makes a stone a gem? It boils down to a few key qualities – beauty and durability. And rarity makes a gem even more special, as is the case for my favourite: painite. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-we-value-diamond-rings-and-other-valentines-day-gifts-89056">Why we value diamond rings and other Valentine's Day gifts</a>
</strong>
</em>
</p>
<hr>
<h2>Tough beauty</h2>
<p>Any stone may become a gem if it has beauty (in the eyes of enough beholders) and is durable enough to retain that beauty through everyday wear. </p>
<p>Durability usually implies that the stone is hard enough to resist abrasion from airborne sand and dust. Also, that it does not easily fracture or “cleave” on flat planes of weakness (determined by its atomic arrangement). </p>
<p>Diamond, the hardest known material, certainly satisfies the abrasion criterion. A diamond crystal does have four orientations of cleavage plane on which it can be split easily. But for diamonds, this apparent liability can be turned into an asset. </p>
<p>The cleavage is used as a short cut in the early stages of shaping, cutting and polishing this extraordinarily hard material, which is otherwise a slow and painstaking business. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/OhFRhfOedXA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How to cleave a diamond.</span></figcaption>
</figure>
<h2>The four Cs</h2>
<p>Demand drives the value of gemstones as commercial items, and this in turn is a function of fashion and name recognition. </p>
<p>However, the main valuation criteria for gems such as diamonds are often summarised as “the four Cs”: <a href="https://www.gemsociety.org/article/gem-pricing-guide-sample/">carats, colour, clarity and cut</a>. </p>
<p>One carat (0.2 g) is the traditional unit of weight for a gemstone – but larger stones are disproportionately rare, and worth more per weight than smaller ones. </p>
<p>While pure diamonds are colourless, and the same is true of many other gem minerals, striking and rare colours almost always increase their value. </p>
<p>Small amounts of impurities or defects of the crystal structure are needed to produce the prized pink diamonds for which the Argyle mine of northwestern Australia is famous. </p>
<p>Impurities also turn the common mineral corundum into its red form (ruby) and other coloured varieties familiar as sapphires. Such colours are appreciated best through the depths of a transparent, intact single crystal, with the passage of light unimpeded by fractures, inclusions or rough surfaces. Hence the value of clarity. </p>
<h2>The rare gem painite</h2>
<p>Although diamonds are still the popular epitome of preciousness, <a href="https://io9.gizmodo.com/5902212/ten-gemstones-that-are-rarer-than-diamond?IR=T">they are far from the rarest minerals to have been used as gems</a>. </p>
<p>As a mineralogist, my favourite amongst these ultra-rare stones comes from the gem gravels of the Mogok region in Myanmar. There, sapphires, rubies, spinels and other gemstones accumulate in river beds after washing down from the surrounding forested hills. These have been mined since ancient times. </p>
<p>In 1957, two deep red stones from a batch donated to the Natural History Museum in London – as shown in the lead image for this story – turned out to be completely new to science. A tiny slice from one crystal was used for research, and the <a href="http://minerals.gps.caltech.edu/files/Visible/painite/Index.html">new mineral was named “painite”</a> after the original donor, the gem dealer Arthur Pain.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/de-beers-to-sell-synthetic-diamonds-heres-how-theyre-made-97558">De Beers to sell synthetic diamonds: here’s how they’re made</a>
</strong>
</em>
</p>
<hr>
<p>A third painite was identified in 1979, but it was not until 2001 that a fourth was found in Myanmar. Efforts to find more intensified, working uphill along creeks and locating progressively less water-worn material. </p>
<p>By 2005, a source outcrop for painite was finally discovered, nearly half a century after the original identification. Several thousand stones have now been recovered, but the small number of cut gems remains the preserve of specialist collectors. </p>
<p>Painite’s extreme rarity is due to it containing the chemical elements zirconium and boron, which do not normally associate with each other in nature and don’t occur together in any other mineral. Ironically, some painite crystals are partly altered to a crust of small pink crystals of the more common ruby. </p>
<p>The increase in supply means that you can now get small crystals of painite pretty easily online for tens of dollars, and poor-quality cut stones for about A$100. However, the tiny proportion of gem-quality stones still fetch <a href="http://www.jewelsdujour.com/2012/08/ten-rarest-precious-stones/">US$60,000 per carat</a>. </p>
<h2>Opal, the odd one out</h2>
<p>The national gemstone of Australia, precious opal, is an anomaly. It is soft enough to scratch easily, <a href="https://www.ajsgem.com/articles/how-care-your-opal-gemstones.html">prone to cracking</a>, most attractive when nearly opaque, and does not occur as crystals.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227121/original/file-20180711-27036-16tz1k7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">A rare example of boulder opal.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/rare-boulder-opal-coober-pedy-australia-1037378152?src=gfrGT4QniUAL0dRvj2X-gw-1-7">from www.shutterstock.com</a></span>
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<p>Opal is made from microscopic spheres of non-crystalline silica in a very regular array. This natural “<a href="http://www.uvm.edu/%7Edahammon/Structural_Colors/Structural_Colors/Opals_And_Photonic_Crystals.html">photonic crystal</a>” diffracts light to produce the play of rainbow colours whose beauty overcomes all other considerations.</p>
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<img alt="" src="https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/227119/original/file-20180711-27018-ss54mj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Opal mining creates health hazards in Coober Pedy, South Australia.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/danger-sign-coober-pedy-south-australia-129058475?src=XEzqJMV1SOiRSajmg5elZw-1-14">from www.shutterstock.com</a></span>
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Read more:
<a href="https://theconversation.com/from-mine-to-wine-creative-uses-for-old-holes-in-the-ground-3245">From mine to wine: creative uses for old holes in the ground</a>
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<h2>Where science comes in</h2>
<p>The polishing and carving of semiprecious stones originated in prehistory. </p>
<p>But the cutting of diamonds in particular has become a sophisticated craft well grounded in the science of optics. One rough stone may ultimately produce several finished stones of different sizes, the pattern of cuts being chosen to minimise waste. </p>
<p><a href="http://www.folds.net/diamond_design/index.html#fig_37">Diamond cutters angle the facets on each stone precisely</a>, so as to maximise the internal reflection of light and the dispersion of white light into rainbow sparkles. They also aim to produce an overall shape which appeals best to the market. </p>
<p>Similar considerations have led to standard cuts being developed for other gems, to show them at their best.</p><img src="https://counter.theconversation.com/content/97453/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Christy does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
What makes a stone a gem? It boils down to a few key qualities: beauty and durability. But opal, the national gemstone of Australia, is an anomaly - it’s soft.
Andrew Christy, Senior Curator (Mineralogy) at the Queensland Museum and Lecturer, The University of Queensland
Licensed as Creative Commons – attribution, no derivatives.