This hefty rock sample includes several different minerals. The dark mass that forms much of the rock is chalcocite (copper sulfide, Cu2S). Chemical reactions with air and water have resulted in the bright blue chrysocola (Cu4H4Si4O10(OH)8) and dark blue azurite (Cu3(CO3)2(OH)2), as well as bright green malachite (Cu2CO3(OH)2). Rocks such as this form in volcanic areas where very hot mineral-laden waters fill cracks in the rock. When the water cools, crystals settle out and form mineral veins in the cracks. Chalcosite and chrysocola are used by mining companies as indicators of copper deposits. This specimen is from the Santa Rita (Chino) copper mine in Grant County, NM.