Crystallography and Structure – the Story of Carbon

BCU Diamond Simulants: Beyond the obvious

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

HPHT: Belt and BARS, toroid presses, cubic presses CVD APHT LPHT Source: YAESS

Source: Apollo Diamonds NPCD

Source: GIA

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!

 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)

Source: GCI

Top: fashioned topaz crystals Bottom: natural diamond crystals

Source: GCI Source: GIA

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.

Flat smooth facet

Sharp, straight edges

Precise junctions

Source: GIA

Two main simulants on the market today:

Cubic zirconia

Synthetic Moissanite

Source: Nathaan gem & Jewellery

Source: Starsgems

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)

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.

Source: GIA

Synthetic Synthetic moissanite moissanite, showing – Optically greater dispersion anisotropic than diamond. (Double refraction)

Source: Callagold

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%

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

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

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

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

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

One of the latest developments onto the market – diamond coatings to the surface of various materials.

Diamond - CZ Diamond - Phenakite Diamond – Synthetic moissanite

The future……? ?