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What is Moissanite? What is Moissanite?

What is Moissanite? What is Moissanite?

What is Moissanite? When a popular artisan who has worked in lapidary since the 1950s suggests taking a closer look at their “grit of choice,” it’s at least worth checking out. Moissanite is a natural mineral that’s also called silicon carbide. Until the late 1980s, it was believed to only be found in grains of primitive chondrictic meteorites pre-dating the formation of our own Sun but with a 9.25 Mohs rating, a close contender in hardness to diamond and now a popular diamond alternative.

Now that’s interesting.

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What is Moissanite?

The mineral is named after French chemist and 1906 Nobel Prize recipient Ferdinand Frédéric Henri Moissan, one of the original members of the International Atomic Weights Committee and designer of the electric-arc furnace, which could attain temperatures upwards of 3,500°C (or 6,332°F).

Moissan’s furnace was used to evaporate substances that were previously considered infusible or impossible to melt. His work in preparing new substances led to the discovery of highly abrasive carborundum. He also pursued his own theory, that diamonds can be synthesized through the crystallization of carbon under pressure by molten iron.

That’s right. Monsieur Moissan is a grandperé of the artificial diamond.

The chemist mistakenly identified moissanite in 1893 when he discovered it in rock samples taken from a meteorite crater near Flagstaff, Arizona. The Barringer Crater Company says that the Earth’s resulting dent is nearly a million feet wide and deep. A meteor estimated to be 300,000 tons with 26,000 mph struck with 150-times the force of Hiroshima. Melted rock fragments and pulverized melted rocks were spread across the desert over a distance of a mile.

Moissan took nearly a decade to correctly determine that the hexagonal plates in his crystals were silicon carbide and not diamond. He did this by measuring the density of the platelets and their inertness towards chemical reactions. This allowed him to establish the existence of the mineral naturally on Earth.

Acheson Process is the name that is used to describe the Acheson Process. It was invented by Edward G. Acheson in the United States, who is also credited with discovering the mineral carborundum. This gritty breakthrough in manufacturing abrasives is credited with advancing the Industrial Age and helped lead to Acheson’s induction in 1997 into the National Inventors Hall of Fame®.

Natural (non-meteor) moissanite was not found until 1958, in the upper mantel of Wyoming’s Eocene-era Green River Formation, and again in 1963 when American Mineralogist reported its presence in inclusions of rare kimberlite in a Yakutia diamond mine in eastern Russia.

But that didn’t necessarily convince Charles Milton, a Fellow of the Geological Society of America and something of a mineralogical dragon slayer, as his 1990 GSA memorial attests:

“Although he enjoyed the detective work involved in the description of a new mineral, he was equally enthusiastic about discrediting mineral species. Charlie became deeply involved with the investigation into moissanite, and its validity as a mineral. He has published more than 50 articles on the subject. Only recently has moissanite (or some polymorph of SiC) been found as a solid inclusion in diamond.”

Take a hike on the rim of Meteor Crater and see the world’s best-preserved meteorite impact site up close!
Courtesy Meteor Crater & Barringer Space Museum

What is Moissanite? What is Moissanite?

Fortunately, the question of what moissanite actually is is not one that most rock tumblers have to deal with. Today, silicon carbide is found in all applications. From diamond alternatives to grinding wheels for lapidary work to its role in the semiconductor business.

Whether sharpening knives or smoothing stones, the “Cadillac of abrasive grits,” as Armour Products refers to silicon carbide, is produced by mixing silica (SiO2) with carbon (C) — basically sand and coal — in electric resistance furnaces at temperatures akin to Moisson: between 1,600°C (2,190°F) and 2,500°C (4,530°F).

The technology manufacturer Arrow ECS says that dark versions of silicon carbide usually contain iron and carbon, while pure SiC crystals, which are formed when silicon carbide sublimes, (changes from a solid to a vapor upon heating and then returns to a solid after cooling), are colorless.

The silicon carbide is then crushed into grits and powders, ranging in size from grits up to powders, for use as sandblasting material, cutting, grinding, and polishing. “Graded” grit contains particles all closely matched in size.

The Barringer Meteor Crater & Space Museum

We’re all made of a little stardust, so while those rocks are tumbling in their silicon carbide, consider a trip to Winslow, Arizona to see and learn more about the crater impact site where Henri Moissan first found his intergalactic namesake. The Crater lies at 5,640’ above sea level, is over a mile wide and 560’ deep, and surrounded by a rim that rises 148’ above the surrounding plains. The middle is filled with eroded sandstone that sits above the crater’s bedrock.

Named a 2021 TripAdvisor Travellers’ Choice and a 2020 Condé Nast Traveller Seven Wonders Of The World, The Barringer Meteor Crater & Space Museum features daily (8 a.m. to 6 p.m.) interactive displays about the Earth and space science, including a 4D movie, Collision! The Barringer Meteor Crater & Space Museum offers daily interactive displays about Earth and space science, including a 4D movie, Collision!

The entrance fee helps to preserve the site and support scientific research in meteoritics. Visit MeteorCrater.com.

You can find more information on the Barringer Crater in this issue, in the Rock Science Section starting on page 68.

But let’s get to the nitty gritty. When it comes to tumbling and finishing, silicon carbide grit rubs everybody – rock tumblers, gem cutters and lapidary artists – the right way.

Why? Why?

  1. It’s hard. The Mohs hardness is greater than nine. This makes it ideal for cutting roughs that are suited to tumble, such as petrified wood, jasper, or agate. The softer materials like sodalite and obsidian need to be tumbled longer than harder rocks such as beryl or topaz.
  2. It is crushed into sharp, angular pieces. This increases the cutting and grinding effectiveness as it tumbles in between rocks.
  3. It’s not expensive. Retail sites like RockTumbler.com cite silicon carbide as selling, as a screened and packaged product, for just a few dollars a pound.
The Barringer Crater was named after Daniel Barringer, the first geologist to prove that an impact crater existed on Earth. Learn why this natural landmark has such importance to the scientific community.
Courtesy Meteor Crater & Barringer Space Museum

The grit size (the larger the number the finer it is) has an impact on both the rock to be polished as well as the strength of the barrel. The most coarse grit, 60/90, is used on rocks in the first tumbler step to smooth rough and sharp edges.

The topic of size prompted a gritty Facebook discussion on a Rock Tumbling & Polishing Group earlier in the summer, regarding 10 pounds of an unidentified but “very coarse” silicon carbide grit one of its members had received for free (can’t get more ‘not expensive’ than that).

Posting a photo of the mystery grit next to a finer but still Stage 1 silicon carbide for comparison, they asked, “Is this stuff useable or is it too extreme?” They guessed the grit size as 10 or 12 and hoped to test it out as a “fast cut” on some “expendable stones” in a dual barrel three-pound tumbler.

Advice tumbled in: “I used stuff that looked like that. On harder rocks, it was amazing. It got them round faster, but it was too fast on softer stones. It scratches the inside of the barrel pretty bad, so I assume it wears out faster.”

“I tried 46/70 in my three-pound tumbler. It did a good job, but left an unsightly surface on delicate stones. So if you want to remove the surface it will probably work, but won’t eliminate the need for using 60/90 as the next stage. And don’t use it on anything delicate. I understand larger barrels create a more aggressive effect due to the weight of rocks pushing down.”

“Coarse grit in three-pound barrels is ineffective, too few particles due to size. It won’t hurt the barrel. I run 45/70 in three-pound barrels for some agates but it’s no faster than 60/90. I use it because I have it!”

“It looks like 36 grit. It won’t wear out barrels any quicker but will not work well in small barrels. I used it for Stage One in 12-pound barrels with Bahia Agate. Overall, pretty useless in small tumblers.”

“I think it would be great to quickly wear down agates with lots of pock marks, etc.”

Henri Moissan (1852-1907), a French chemical engineer, used a Moissan Chaplet arc electric furnace to try and synthesize diamonds.
Courtesy Public Domain US/US Library of Congress Prints & Photographs

Time to Shine

Henri Moissan, 130 years ago, probably did not think about tumbling as he derived silicon carbonate from samples of iron meteorites in the Arizona Desert. But his patient approach to what is moissanite and shining a light on scientific inquiry is not so different from today’s methodical steps toward shining stones:

“The advancement of science is slow; it is effected only by virtue of hard work and perseverance.”

You might want to add… a little grit.

This article about moissanite was previously published You can also find out more about the following: Rock & Gem magazine. Subscribe here. Story by L.A. Sokolowski.

What is Moissanite? Exploring This Silicon Carbide first appeared on Rock & Gem Magazine.

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