I've been learning a lot about the gems and minerals that are used to make the jewelry I love and that I talk about regularly here at Larson Jewelers. I get asked a lot of questions about things like the hardness of gems or how brittle different minerals are, so I decided to talk about some of the hardest gems and minerals found on Earth. There are thousands of minerals - more than 4,000, in fact - that occur naturally in the world, with the most common class of minerals being silicates.
One of the methods used to measure mineral hardness, and one that is regularly used to classify gems and minerals, is the Mohs scale. The Mohs scale was created by Friedrich Mohs, a German geologist and mineralogist, in 1812. The more minerals that can scratch the mineral being tested, the lower its number on the Mohs scale. Harder minerals will be able to scratch those that are softer. Below I will discuss the hardest gems and minerals found on the planet, according to the Mohs scale.
Diamond: 10 on the Mohs scale
Diamonds are loved for many reasons, including their resistance to wear and tear. As the hardest mineral found on earth, diamonds are the least likely to change with time. They form under incredibly high pressure, way beneath the Earth's surface - hundreds of miles beneath the surface, in fact!
Boron: 9.5 on the Mohs scale
This chemical element is produced by something called cosmic ray spallation, which is a type of nuclear fission that occurs naturally. Its naturally occurring compounds are more common than boron in its purest form. Boron compounds are used for a variety of purposes, including in fiberglass insulation, bleaches, and silica-based glasses to provide thermal shock resistance.
Stishovite: 9.5 on the Mohs scale
Very hard and very dense, stishovite was first synthesized by Russian physicist Sergey M. Stishov in 1961 and was found in a meteorite impact site by Edward C.T. Chao in 1962. Through the application of hydrogen fluoride, stishovite can be separated from quartz.
Moissanite: 9.25 on the Mohs scale
Thanks to its rarity, moissanite wasn't introduced to the jewelry market until 1998. It's very comparable to diamonds but with a lower price, and it's therefore often sought as a diamond alternative.
Titanium Carbide: 9-9.5 on the Mohs scale
Very resistant to corrosion, wear, and oxidation, titanium carbide is often used to coat watches, in tool bits, and sometimes as a heat shield for spacecraft to allow for atmospheric re-entry.
Corundum: 9 on the Mohs scale
A naturally clear transparent rock-forming mineral, corundum is a form of aluminum oxide with traces of titanium, chromium, and iron. Because of how hard it is, it is able to scratch almost all other minerals. It is used commonly as an abrasive.
Tungsten Carbide: 9 on the Mohs scale
Very hard, tungsten carbide is used for a variety of purposes, including jewelry. When used in jewelry, it is often incorrectly simply called tungsten, even though tungsten carbide actually consists of equal parts tungsten and carbon. It has become as popular as it is in the jewelry industry due to its resistance to scratching and extreme hardness.
Chrysoberyl: 8.5 on the Mohs scale
This natural gemstone is interesting because of its cyclic twins called trillings. The twinned crystals look sort of hexagonal in appearance and are usually greenish-yellow in color, though various shades of green, brown, yellow, and other colors exist.
Cubic Zirconia: 8.5 on the Mohs scale
The first discovery of a naturally occurring cubic zirconia was made in 1937 by German mineralogists K. Chudoba and M.V. Stackelberg. They found it within metamict zircon in the form of microscopic grains and did not think it important enough to name at the time. Today, cubic zirconia is mass produced in the jewelry marketplace. Because cubic zirconia so rarely occurs naturally, the cubic zirconia found in jewelry is created or synthesized by humans.
Chromium: 8.5 on the Mohs scale
Not only is chromium very hard, but it also has a very high melting point. It is brittle and lustrous, taking a high polish and able to resist tarnishing. It was first used during the Qin dynasty over 2,000 years ago by the Chinese as a coating for the metal weapons that were found with the Terracotta Army.
I hope you found this as interesting as I did! I'm finding that the more I learn about minerals and gems, the more I feel the need to research. Let me know if you have anything to add! I'd love to read any interesting facts you want to share.
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