These are lab created colorless YAG garnet facet rough. Smaller pieces can be purchased by weight range and larger pieces are labelled with their gram weight and letter in the photo and they can be purchased individually.
This is a very cool gem, a type of lab-created garnet grown for use in scientific applications, YAG (Yttrium Aluminum Garnet). It has the same structure as a natural garnet but a composition which could never occur in nature, allowing it to have a higher hardness (8.25) and greater brilliance.
YAG is an ideal crystal for scientific applications: it is hard, durable, relatively easy to grow and can be doped with a wide variety of ions to give it a wide variety of properties. It is widely used as a laser and scintillator crystal but also in more niche applications like optics. I am not sure what this material was grown for--it is colorless and either undoped or doped with something that does not affect the color. Nevertheless it serves as a bright and beautiful gem which was once used as a stand-in for diamond.
YAG is an excellent material to facet, incredibly easy to cut and polish and with a high hardness of 8.25-8.5, an RI of 1.83 and good dispersion which makes for very lively stones even before the color factors in. It is suitable for use in all kinds of jewelry.
