BGO12 Bismuth Germanate Facet Rough pyro showing a silky chatoyance caused

showing a silky chatoyance caused by twinning

Note that the camera exaggerates the red at the expense of the green--they do look better in person

and Nd alone gives a purple shifting color

Most of these have voids inside

The blue also gets more vivid--the frosted faces make it look greyer than it is

BGO12 Bismuth Germanate Facet Rough pyro showing a silky chatoyance causedThese 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