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Crystallography and Structure – the Story of Carbon

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Crystallography and Structure – the Story of Carbon BCU Diamond Simulants: Beyond the obvious © BCU/ASF 2017 BCU Diamonds: The most sought after material on the planet, and the only gemstone to be made of one single element. The strongest of bonds, formed only under intense heat and pressure can turn carbon into diamond…..without these, it’s simply coal. Temperature: > 900oC Pressure: 45Kbar “Perhaps times definition of coal is the diamond” (Khalil Gibran) Source: Junkee.com © BCU/ASF 2017 BCU Synthetic diamond: Various different methods have been employed to create synthetic diamonds, which, in most cases, can’t be identified without advanced lab equipment. HPHT: Belt and BARS, toroid presses, cubic presses CVD APHT LPHT Source: YAESS Source: Apollo Diamonds NPCD Source: GIA Source: GIA © BCU/ASF 2017 BCU Imitations: Just because it looks and shines like a diamond doesn’t necessarily make it one. (Edmond Mbiaka) A simulant/imitation is a natural or synthetic material that is used to imitate the effect, colour, and appearance of another gem material (diamond) without possessing the same chemical and physical properties. As diamond is the most sought after of gems, there have been innumerable attempts to imitate it, with varying degrees of success! © BCU/ASF 2017 BCU Imitations/Simulants Common simulants include; Cubic Zirconia Synthetic Moissanite Less common simulants include; Quartz (natural or synthetic) Pollucite Bismuth germinate Sapphire (natural or synthetic) Synthetic rutile Lithium niobate Topaz Strontium titanate Synthetic forsterite Spinel (natural or synthetic) Yttrium aluminium Garnet-topped doublets Zircon garnet (YAG) Glass/paste Gadolinium gallium garnet (GGG) © BCU/ASF 2017 BCU Topaz….. Source: GCI Source: GCI Top: fashioned topaz crystals Bottom: natural diamond crystals Source: GCI Source: GIA © BCU/ASF 2017 BCU Diamond Easiest way to spot an imitation…… know what a diamond looks like! Only a diamond looks like a diamond – all imitations have Source: Shutterstock features that help differentiate them. © BCU/ASF 2017 BCU Diamond Flat smooth facet Sharp, straight edges Precise junctions Source: GIA © BCU/ASF 2017 BCU The simulants: Two main simulants on the market today: Cubic zirconia Synthetic Moissanite Source: Nathaan gem & Jewellery Source: Starsgems © BCU/ASF 2017 BCU Cubic Zirconia This simulant was introduced in the 1970’s, as an inexpensive diamond imitation. It is a zirconium oxide, stabilised to maintain a cubic form by the addition of various elements such as calcium, yttrium and neodymium, some of which can also add colour to the stone. Source: Syntheticgems.org Source: A.S.Fellows Source: Syntheticgems.org © BCU/ASF 2017 BCU Detection: • Differentiating between CZ and diamond is a task usually accomplished with the 10x loupe. Important factors include; • Poor faceting (rounded edges, misaligned facets) NB Can be cut extremely accurately! • Lack of inclusions • Colourless (D) through to fancy colour • Girdle condition on a CZ is usually ground, which creates identifiable grinding lines. • Lower lustre (bright vitreous as opposed to adamantine) • Higher fire/dispersion – 0.058 to 0.066 • Greater density – 5.6 to 6.0 • Lower thermal conductivity (thermal tester) © BCU/ASF 2017 BCU Features: Rounded facet edges, misaligned junctions, Source: Gem-A Grinding lines on girdle Source: GIA © BCU/ASF 2017 BCU Synthetic Moissanite First seen in gem quality in 1998, synthetic moissanite is the gem quality version of Silicon carbide, more commonly known as the industrial abrasive, carborundum (used since 1893). Source: Mindat Source: JTV Source: Mindat © BCU/ASF 2017 BCU Detection: • Differentiating between synthetic moissanite and diamond is a task again usually accomplished with the 10x loupe. Important factors include; • High degree of double refraction, dependent upon viewing angle. • Thin hair/thread-like inclusions, running perpendicular to the table, • Increased fire (due to double refraction) – 0.104 • Similar SG to diamond - 3.22 • Girdle is usually polished, to reduce the number of facet edges to be optically doubled. • Overlapping thermal conductivity with diamond but synthetic moissanite is an electrical conductor, whilst diamond is an insulator. © BCU/ASF 2017 BCU Detection: Thin parallel growth Diamond – tubes in synthetic Optically moissanite isotropic Source: GIA Synthetic Synthetic moissanite moissanite, showing – Optically greater dispersion anisotropic than diamond. (Double refraction) Source: Callagold © BCU/ASF 2017 BCU Other Simulants: Over the years, many other materials have been use to imitate diamonds, but few have been as popular as CZ or Synthetic moissanite…….these include: Glass/paste: Synthetic Spinel Synthetic Sapphire Dispersion: 0.041. Dispersion: 0.020. Dispersion: 0.018. Reflectivity: 4% Reflectivity: 7.1% Reflectivity: 7.6% Source: JTV Source: GIA Source: GIA © BCU/ASF 2017 BCU Other Simulants: Source: GIA Over the years, many other materials have been use to imitate diamonds, but few have been as popular as CZ ands Synthetic moissanite…….these include: Zircon: Strontium titanate Lithium niobate Dispersion: 0.039. Dispersion: 0.190. Dispersion: 0.130. Reflectivity: 8.3% Reflectivity: 17.1% Reflectivity: 15.5% Source: GIA Source: JTV Source: JSG © BCU/ASF 2017 BCU Other Simulants: Over the years, many other materials have been use to imitate diamonds, but few have been as popular as CZ ands Synthetic moissanite…….these include: Yttrium aluminium Gadolinium gallium Bismuth germinate garnet (YAG) garnet (GGG) Dispersion: 0.029. Dispersion: 0.028. Dispersion: 0.045. Reflectivity: 19.3% Reflectivity: 8.6% Reflectivity: 10.7% Source: JSG Source:Source: JSG JTV Source: JSG © BCU/ASF 2017 BCU Other Simulants: Over the years, many other materials have been use to imitate diamonds, but few have been as popular as CZ ands Synthetic moissanite…….these include: Synthetic rutile: Phenakite: Synthetic forsterite: Dispersion: 0.280. Dispersion: 0.015. Dispersion: 0.020. Reflectivity: 20% Reflectivity: 6% Reflectivity: 6% Source: JTV Source: Gemdat Source: GIA © BCU/ASF 2017 BCU Other Simulants: Over the years, many other materials have been use to imitate diamonds, but few have been as popular as CZ ands Synthetic moissanite…….these include: Danburite: Topaz: Pollucite: Dispersion: 0.017. Dispersion: 0.014. Dispersion: 0.012. Reflectivity: 5.7% Reflectivity: 5.4% Reflectivity: 4.1% Source: GIA Source: JTV Source: GIA © BCU/ASF 2017 BCU Composites: Besides single material imitations, multi-layered materials have been used to create the appearance of singe stones. Diamond - Diamond: Corundum - Strontium Titanate Synthetic Spinel – Strontium Titanate Synthetic Spinel – Lithium Niobate Garnet-topped Doublet © BCU/ASF 2017 BCU Coatings: One of the latest developments onto the market – diamond coatings to the surface of various materials. Diamond - CZ Diamond - Phenakite Diamond – Synthetic moissanite © BCU/ASF 2017 BCU The future……? ? © BCU/ASF 2017.
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