Pegmatite black tourmalinePegmatitewith black tourmaline.
Intrusive igneous rock of felsic composition.
The black tourmaline crystals are imbedded in a very coarse crystalline matrix of quartz (clear gray) and plagioclase feldspar (white)
Pegmatite dikes like this are not uncommon in the Peninsular Ranges of Southern California. They are associated with Alaskite dikes that formed in the fluid-rich, late-stage cooling of large granitic intrusions.
Vulcan Mountains, San Diego, CA 2/2/2021