Purple dumortierite in a light colored quartz groundmass, from the Dehesa Dumortierite deposit, Alpine, Laguna Mts, San Diego Co., California. The small, needle-like dumortierite crystals show a crisp blue/white fluorescent response under short wave UV. Dumortierite is a fibrous aluminium boro-silicate mineral. The size of this specimen is 44 x 29 x 18 mm.
Photo on left was taken under short wave UV (254nm). Visible light photo on right.