How Is Moissanite Made?
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Background
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Swedish chemist Jons Jacob Berzelius, the discoverer of silicon, theorized in 1824 that a compound of silicon and carbon may exist. To prove his theory, he synthesized the compound. In 1893, French chemist Ferdinand Moissan inspected samples of dirt from a meteor crater in Canyon Diablo in Winslow, Arizona. He found crystals he initially identified as diamonds. In 1904, he announced he had found a new mineral instead--Berzelius's silicon-carbide (SiC). It was given the mineral name moissanite in his honor.
Chemists discovered more than 250 versions, or polymorphs, of silicon-carbide. Initial uses involved abrasives. It was used in early radios. In 1907, Henry Joseph Round produced the first light emitting diode (LED) from silicon-carbide.
Moissanite as Jewel
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Moissanite poses a significant challenge as a jewel. It's plentiful in meteorites, extremely rare on earth. Also, naturally occurring moissanite forms very small crystals. Chemists could synthesize silicon-carbide but only in colors and in fairly small sizes.
Moissanite not only has many polymorphs, it has more than 100 polytypes. Each polytype has the same chemical composition as the others, but it has a unique crystal structure. Chemists theorized they could produce gem quality silicon-carbide if they could synthesize a 6H polytype, a crystal with six double layers of silicon and carbon atoms.
A chemist named Lely developed a process that came close in 1955. The Lely process vaporized and condensed silicon-carbide without it passing through a liquid state. At 2500 degrees C it produced large single crystals, but did not control for impurities so the crystals were not clear. A chemist named Davis came closer in 1990 by heating silicon-cabide vapor to 2300 degrees C in a vacuum, then cooling it to 2200 degrees C in low-pressure argon.
Then Cree Research, of Durham, North Carolina, improved the process to produce clear, large single crystals. The company specializes in semiconductors and LEDs. So, in 1995 it created Charles and Colvard jewelers in Morrisville, North Carolina. Cree produces the crystals. Charles & Colvard have them cut and market them as moissanite jewelry. Together they own the patent for moissanite and are the exclusive, world-wide producer and distributor.
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How Moissanite Rates
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Jewelers grade gem stones on four factors. Moissanite scores better than diamonds on three of them. It has a fire dispersion of .104 to diamond's .044. Its brilliance has a rating of 2.65 to diamond's 2.42. Jewelers measure its luster at 20.4 percent to diamond's 17.2 percent. The hardness scale is based on the hardness of a diamond at 10. Moissanite has a hardness of 9.25. Moissanite has one disadvantage as a gem. It's birefringent. Under certain conditions it may give the viewer a sense of double vision. Charles & Colvard controls the cutting and polishing process to eliminate birefrigence.
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