Opaque Neon Yellow YAG.  Yttrium aluminum garnet (YAG, Y3Al5O12) Lab created garnet with a RI of 1.833 and 8.5 hardness, making it suitable for everyday jewelry. YAG is also known for its fabulous dispersion.  Sourced from Kazakhstan.⁠ 

Photo of finished cabochon provided for reference

44.13 grams / 220 carats / 35 x 20 x 14 mm