Yb:YAG. The color is absolutely in aqua’s wheelhouse. In fact, I’ve come to think of this particular Yb:YAG as more aquamarine than aquamarine can be. That is because it has an impressive RI of 1.83 (aqua is 1.57) and hardness of 8.25 on the Mohs scale (tucking it just under sapphire) and a dispersion value of .033 (to diamond’s .044, so not too shabby for a garnet).
Most Yb:YAG is annealed (heated) when it is intended for laser use. Annealing usually removes all the blue color from Yb:YAG, but this laser rod was not annealed. Most of the other blue Yb:YAG one finds in the market today was created in China for gem cutters. Its blues are much more vibrant, but this material was cut from a laser rod and is of the same optical standard used in lasers. That means the quality of its crystal is very high, and this particular material is a bit of a unicorn.
We have added a photo of a finished gem that was cut from the same laser rod. These pictures are from the rod, but may not be the actual 17.7 piece, but that piece is a half moon and looks the same.
Total Weight grams: 3.54
Total Weight Carats: 17.7
14.4x 7.11x 9.48
Notes: Laser quality clarity
Color: Light blue/aqua color