This colorful specimen contains blue-green, fibrous rosasite crystals, collected from the Ojuela Mine in Durango, Mexico. The rosasite formed in fibrous masses, branching from the limonitic matrix. Translucent and colorless selenite crystals fan out from the rosasite and limonitic matrix, as well.
Rosasite is a secondary mineral that forms in oxidation zones of copper-zinc deposits, generally forming a fibrous botryoidal sphere that can appear vitreous and silky. While typically featuring a blue-green color, colorless specimens are not unheard of. The chemical formula of rosasite is CuZnCO3(OH)2.