BGO12 Bismuth Germanate Facet Rough pyro 1x 80 degree index gear

1x 80 degree index gear (ideal for cutting D20s)

Most of these have voids inside

and Nd alone gives a purple shifting color

larger than a hen's egg and about the size of a duck egg

BGO12 Bismuth Germanate Facet Rough pyro 1x 80 degree index gearThese are BGO 12 aka Bismuth Germanate facet rough. This is a real cool rarity in the gem world. Bismuth Germanate (in this case, specifically Bi3Ge4O12 aka evlitine) is valued as an optical substrate because of its highly unusual electrooptical properties. It has exceptionally good optical properties too, with (as far as we can tell the literature is weak) an RI of 2. 15 and dispersion of 0. 1. Cut stones are incredibly beautiful with high brilliance