Azurite

Quite by accident while driving in the mountains today , we discovered an abandoned mine area.  Primarily, we collected Azurite and by the time the sun drove us out of the locale, our assembled assortment  looked like we spent an afternoon hand painting rocks.  Doing a quick bit of research, I learned that this mineral has been used to make paint pigment ... no doubt special to dip a paint brush in such a brilliant display of blue and green.

theworldinlight.com

Azurite is a secondary copper mineral and historicallyhas been ground into a powder and used as paint pigment (Polk, Patti. Collecting Rocks, Gems and Minerals;244)