ABSTRACT
Crystal form: Columnar with curved faces Refractive index: 2.15-2.18 (depending on amount of stabilizer) Dispersion: Very high (0.065) Specific gravity: 5.6-6.0 (depending on amount of stabilizer) Hardness: 8.5 Lustre: Adamantine Luminescence: Green-yellow to yellow in SW UV, whitish in X-rays Absorption spectrum: Strong rare earth spectrum in pink, lilac and orange-brown
stones; deep-red stones (coloured by cerium) have a strong band in the yellow at 575 nm, and a complete absorption of the spectrum from 560 nm to the violet end; purple stones have three bands in the orange, yellow and green
Synthesis process: Skull crucible
Gadolinium gallium garnet (GGG) Composition: Gd3Ga5O12 Crystal system: Cubic Crystal form: Columnar with 3 inch (7.5 cm) diameter (originally produced as a
substrate for computer bubble memories) Colour: Colourless (diamond simulant), red (manganese), yellow (praseodymium),
lilac (neodymium), green (chromium or cobalt), red (manganese) Refractive index: 1.97 Dispersion: High (0.045) Specific gravity: 7.05 Hardness: 6.0 (brittle) Lustre: Subadamantine Luminescence: Colourless stones fluoresce peach colour in SW UV (if exposed
for several minutes stones turn brown, but return to colourless after several hours). Stones fluoresce lilac in X-rays
Absorption spectrum: Coloured stones show the appropriate transition element or rare earth spectrum
Synthesis process: Czochralski crystal pulling
Lithium niobate Composition: LiNbO3 Crystal system: Trigonal Crystal form: Large columnar Colour: Colourless (diamond simulant), red (iron), yellow (nickel or manganese),
green (chromium), blue-violet (cobalt) Refractive index: 2.21-2.30
