YAG - Yttroaluminate

YAG: Yttroaluminate Y3Al5O12; (not related to garnet); Cubic symmetry; Relative Density: 4.57-6.69 heavy; Small Dispersion:0.028; Refractive Index: 1.83; Good Hardness:8.5; Grown by flux melt method and used widely in the early 1970's to be replaced later by Cubic Zirconia.

This was first marketed in 1969, being made famous when Richard Burton had a copy of a 69 carat pear shaped diamond given to his wife, Elizabeth Taylor, made in YAG. It is quite hard, loups clean, and is singly refractive like diamond. It has less fire than diamond, but when cut with slightly different facet angles, starts to approach a good diamond look-a-like. These newly cut stones were marketed under the name 'Diamonaire'. It is relatively hard and holds a good polish with an adamantine lustre. It has a high relative density, and when weighed is clearly too heavy for an equivalent cut in diamond. A 1.00 carat stone measured on a Moe's gauge would weigh around 1.30cts on a balance. An immersion test in refractive liquids, will reveal its lower refractive index.

Original document: http://www.jewellerycatalogue.co.uk/diamonds/simulants_info.php