These are lab created green laser garnets, aka CTH YAG. The pieces are labelled with their letters and weights and can be purchased individually. We also have laser rods from the same material available--they are very beautiful scientific curiosities.
This is a classic laser gem, CTH YAG. Like normal Cr YAG (aka Christmas Garnet) it has a super rich green base color, but the addition of . This means the base color does not have to compete with a red glow and comes out even richer and purer, easily matching and exceeding any other green gem I have seen in color (and I don't say that lightly!). It also has excellent brilliance, and with a hardness of 8.5 is great for use in all kinds of jewelry.
CTH YAG is used in far infrared lasers for a variety of purposes including medical procedures and meteorological measurements. Fortunately for us though it was designed for science when they grow crystals there are areas that are unusable, and we were able to get these offcuts to have made into gems.