Moissanite

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Moissanite
Moissanite-USGS-20-1001d-14x-.jpg
General
Category Mineral species
Formula
(repeating unit)
SiC
Strunz classification 01.DA.05
Identification
Color Transparent, green, yellow
Crystal habit Generally found as inclusions in other minerals
Crystal system Most common: 6H hexagonal (6mm), space group: P63mc
Cleavage (0001) indistinct
Fracture Conchoidal – fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz)
Mohs scale hardness 9.5
Luster Adamantine to metallic
Streak greenish gray
Diaphaneity transparent
Specific gravity 3.218–3.22
Refractive index nω=2.654 nε=2.967, Birefringence 0.313 (6H form)
Ultraviolet fluorescence green or yellow
Melting point 2730 °C (decomposes)
Solubility none
Other characteristics Not radioactive, non-magnetic
References [1][2][3]

Moissanite /ˈmɔɪsənt/[4] originally referred to a rare mineral discovered by Henri Moissan having a chemical formula SiC and various crystalline polymorphs. Earlier, this material had been synthesized in laboratories and named silicon carbide (SiC).

Background[edit]

Mineral moissanite was discovered by Henri Moissan while examining rock samples from a meteor crater located in Canyon Diablo, Arizona, in 1893. At first, he mistakenly identified the crystals as diamonds, but in 1904 he identified the crystals as silicon carbide.[5][6] The mineral form of silicon carbide was named moissanite in honor of Moissan later on in his life. The discovery in the Canyon Diablo meteorite and other places was challenged for a long time as carborundum contamination from human abrasive tools.[7]

Geological occurrence[edit]

Until the 1950s no other source, apart from meteorites, had been encountered. Later moissanite was found as inclusion in kimberlite from a diamond mine in Yakutia in 1959, and in the Green River Formation in Wyoming in 1958.[8] The existence of moissanite in nature was questioned even in 1986 by Charles Milton, an American geologist.[9]

Moissanite, in its natural form, is very rare. It has only been discovered in a small variety of places from upper mantle rock to meteorites. Discoveries have shown that moissanite occurs naturally as inclusions in diamonds, xenoliths, and ultramafic rocks such as kimberlite and lamproite.[7] They have also been identified in carbonaceous chondrite meteorites as presolar grains.[10]

Meteorites[edit]

Analysis of SiC grains found in the Murchison carbonaceous chondrite meteorite has revealed anomalous isotopic ratios of carbon and silicon, indicating an origin from outside the solar system.[11] 99% of these SiC grains originate around carbon-rich Asymptotic giant branch stars. SiC is commonly found around these stars as deduced from their infrared spectra.

Composition[edit]

All applications of silicon carbide today use synthetic material, as the natural material is very scarce. Silicon carbide was first synthesized by Jöns Jacob Berzelius, who is best known for his discovery of silicon.[12] Years later, Edward Goodrich Acheson produced viable minerals that could substitute diamond as an abrasive and cutting material. This was possible as moissanite is one of the hardest substances known, with a hardness below that of diamond and comparable with those of cubic boron nitride and boron. Since naturally occurring moissanite is so rare, lab-grown moissanite is the only commercially viable version of the mineral. More recently, pure synthetic moissanite has been made from thermal decomposition of the preceramic polymer poly(methylsilyne), requiring no binding matrix (e.g. cobalt metal powder).

Physical properties[edit]

Main article: Silicon carbide

The crystalline structure is held together with strong covalent bonding similar to diamonds,[5] that allows moissanite to withstand high pressures up to 52.1 gigapascals.[5][13] Colours vary widely and are graded in the I-J-K range on the diamond color grading scale.[14]

Applications[edit]

Gem-cut synthetic moissanite set in a ring

Moissanite was introduced to the jewelry market in 1998.[15] It is regarded as a diamond alternative, with some optical properties exceeding those of diamond. Its lower price, and less exploitative mining practices necessary to obtain it, makes it a popular alternative to diamonds. Due in part to the similar thermal conductivity between moissanite and diamond, it is a popular target for scams; however, an electrical conductivity test (with a check for birefringence) should alert any buyer to fraud. On the Mohs scale it is a 9.5, with a diamond being a 10.[3] Moissanite is stronger than sapphire or ruby. In many developed countries, the use of moissanite in jewelry has been patented; these patents expire in 2015 for the US, and 2016 in other countries.[16][17][18] Moissanite gemstones are sometimes marketed under the trademark Berzelian, a reference to the work of Berzelius on SiC.

Because of its hardness, it can be used in high-pressure experiments, as a replacement for diamond (see diamond anvil cell).[5] Since large diamonds are usually too expensive to be used as anvils, synthetic moissanite is more often used in large-volume experiments. Synthetic moissanite is also interesting for electronic and thermal applications because its thermal conductivity is similar to that of diamonds.[13] High power SiC electronic devices are expected to find use in the design of protection circuits used for motors, actuators, and energy storage or pulse power systems.[19]

See also[edit]

References[edit]

  1. ^ Moissanite at Webmineral
  2. ^ Moissanite at Mindat
  3. ^ a b Moissanite in Handbook of Mineralogy
  4. ^ "Moissanite". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. 
  5. ^ a b c d Xu J. and Mao H. (2000). "Moissanite: A window for high-pressure experiments". Science 290 (5492): 783–787. Bibcode:2000Sci...290..783X. doi:10.1126/science.290.5492.783. PMID 11052937. 
  6. ^ Henri Moissan (1904). "Nouvelles recherches sur la météorité de Cañon Diablo". Comptes rendus 139: 773–786. 
  7. ^ a b Di Pierro S., Gnos E., Grobety B.H., Armbruster T., Bernasconi S.M., and Ulmer P. (2003). "Rock-forming moissanite (natural α-silicon carbide)". American Mineralogist 88: 1817–1821. 
  8. ^ J. Bauer J. Fiala, R. Hřichová (1963). "Natural α–Silicon Carbide". American Mineralogist 48: 620–634. 
  9. ^ H. E. Belkin, E. J. Dwornik (1994). "Memorial of Charles Milton April 25, 1896 – October 1990". American Mineralogist 79: 190–192. 
  10. ^ T. Yokoyama , V. K. Rai , C. M. O’D. Alexander , R. S. Lewis , R. W. Carlson , S. B. Shirey , M. H. Thiemens , and R. J. Walker (March 2007). "Nucleosynthetic Os Isotopic Anomalies in Carbonaceous Chondrites". 38th Lunar and Planetary Science Conference. 
  11. ^ The Astrophysical Nature of Silicon Carbide
  12. ^ Saddow S.E and Agarwal A. (2004). Advances in Silicon Carbide Processing an Applications. Artech House Inc. ISBN 1-58053-740-5. 
  13. ^ a b Zhang J., Wang L., Weidner D.J., Uchida T. and Xu J. (2002). "The strength of moissanite" (PDF). American Mineralogist 87: 1005–1008. 
  14. ^ Read P. (2005). Gemmology. Massachusetts: Elsevier Butterworth-Heinemann. ISBN 0-7506-6449-5. 
  15. ^ "Moissanite Rights". Professional Jeweler Magazine. May 1998. Retrieved 24 October 2012. 
  16. ^ "Patent US5762896 - Silicon carbide gemstones - Google Patents". Google.com. Retrieved 2014-02-01. 
  17. ^ "Patent US5723391 - Silicon carbide gemstones - Google Patents". Google.com. 1995-08-31. Retrieved 2014-02-01. 
  18. ^ "Moissanite Gem Patent Restrictions by Country and Year of Expiration". 
  19. ^ Bhatnagar, M.; Baliga, B.J. (1993). "Comparison of 6H-SiC, 3C-SiC, and Si for power devices". IEEE Transactions on Electron Devices 40 (3): 645–655. Bibcode:1993ITED...40..645B. doi:10.1109/16.199372. 

Further reading[edit]