As geo-fanatics, we might see the stones designated as “precious gems” to be rather boring compared to the much rarer, more beautiful minerals out there, but there’s more to these mainstream gems than meets the eye!
From Mineral to Gem
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You know the four precious stones—highly valuable and prized for their dazzling sparkle and clarity—but do you know where they come from?
Diamonds
Diamonds form under extreme pressure and temperature at depths of 140 to 190 km in the Earth's mantle. Carbon atoms crystallize in a cubic structure, and volcanic eruptions bring these diamonds to the surface via kimberlite and lamproite pipes.
Major diamond mining regions include South Africa, Russia, and Canada. Mining usually involves open-pit or underground mining of kimberlite pipes. Recently, marine mining has gained traction, especially off Namibia's coast, where diamonds are extracted from the seabed.
Emeralds
Emeralds form in hydrothermal veins within metamorphic rocks, crystallizing from silica-rich, beryllium-laden fluids. Chromium and vanadium give these verdant gems their signature color, differentiating them from other beryls.
Major sources of emeralds include Colombia, Zambia, and Brazil. Open-pit mining is common, involving large-scale earth removal to access emerald-bearing rock. Zambia’s Kagem Emerald Mine, the largest globally, produces 25–30 percent of the world’s gem-quality emeralds.
Sapphires
Sapphires form in igneous and metamorphic rocks under high-pressure and high-temperature conditions. Composed of corundum (aluminum oxide), their blue color comes from trace amounts of titanium and iron. They are commonly found in marble and basalt, and can even have volcanic origins.
Significant deposits are found in Myanmar, Sri Lanka, and Madagascar. Mining methods include traditional alluvial mining, sifting through riverbed sediments, and mechanized mining, involving drilling and blasting rock to access sapphire deposits.
Rubies
Rubies form under high-pressure conditions in metamorphic rocks such as marble. Ideal formation involves significant heat and pressure, often linked to tectonic activity. Set apart from other corundums such as sapphire, rubies’ color is due to trace amounts of chromium.
Key sources include Myanmar, Thailand, and Mozambique. Mining methods range from open-pit mining, which removes surface layers, to underground mining with shafts and tunnels.
In addition to their beauty, rubies also have value in the medical field due to their optical properties… Read on to find out how!
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We tend to think of precious gems as different than “ordinary” minerals, hence why they’re so prevalent in jewelry and seen as status symbols of the wealthy. However, these minerals hold more than just monetary value!
Surgical lasers:
Ruby lasers, which use synthetic ruby crystals as the gain medium, were first used in medical procedures in the 1960s. The first medical laser successfully destroyed a retinal tumor, marking a significant advancement in laser surgery.
While largely replaced by advanced systems, ruby lasers remain valuable in specific medical applications. Their precise wavelength and ability to target pigmented tissues make them useful in certain dermatological and optometric procedures.
Watch faces:
When you think of minerals in watches, your mind goes to quartz and piezoelectricity, right? Well, there’s another gem that’s commonly used in watches: sapphire! Although technically synthetic, sapphire is a key component of glass watch faces.
Sapphire glass production involves crystallizing aluminum oxide at high temperatures to create a transparent crystal. Known for its exceptional clarity and durability, sapphire glass enhances watch dial visibility, making it ideal for luxury and high-end watches.
Abrasives:
The same high hardness and durability that makes gems a sought-after choice for jewelry is what also makes them good abrasives! Gems such as corundum, garnet, olivine, and even diamond, have various industrial applications.
These gems’ tiny, sharp edges can smooth, shape, clean, and drill a variety of surfaces. Though often synthetic, the gems are ground up into small grains and used to make sandblasting medium, sandpaper, or drill bits. Now that’s what I call cutting-edge technology!
And… sobriety talisman?
You read that right! Though a common stone today, amethyst was considered a precious gem in Ancient Greece. It was as expensive as rubies and emeralds and was prized for its beauty and its connection to Bacchus, the god of wine.
Amethyst is derived from the Greek “amethystos,” meaning “not drunken,” and was believed to ward off drunkenness. The stone was often made into amulets or carved into cups to neutralize the intoxicating effects of wine.
Just so we’re clear… this is indeed a myth, so drink responsibly no matter the receptacle!
I hope you enjoyed this week’s edition of GeoLifestyle!
Unique applications of gems are a fun topic for me! I’m not much of a sparkly jewelry wearer, but I have talked extensively about engagement rings, particularly alternatives to diamonds. I even made a popular video series about it a couple of years ago!
Also, I’d like to thank the AAPG newsletter editorial team for filling in for me while I was sick last week. I’m feeling much better now and so glad I got to write this edition for you all!
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