These are lab-created LuAG (Lutetium Aluminum Garnet) facet rough. Each is labelled with its gram weight and letter in the photo and they can be purchased individually.
LuAG is an exotic lab-created crystal with the same structure as natural garnets, but a composition and properties which are impossible in nature. While the most famous type is the neon green cerium-doped LuAG, when doped with praseodymium instead you get this very odd multifluorescence: longwave UV gives a pale green, shortwave gives violet and best of all blue light gives a strong orange glow. This means that against a black background in blue-leaning lighting you have a light green stone with a visible orange glow--very uncanny!
Pr:LuAG, like its more famous brother Ce:LuAG, is used as a scintillator in high end applications.
LuAG facets similarly to YAG (Yttrium Aluminum Garnet) - ie: pretty much perfectly and easily without much complaint. It has a hardness of 8.5 and no durability issues. It has very good optical properties with an RI of 1.83, just slightly better than yag.
