Pyrolusite on Chocolate Limestone, from Morocco (Ref 2620)

Pyrolusite is usually found as matte-black powdery to fibrous crusts, sometimes in botryoidal aggregates or columnar, more rarely as druzes of small prismatic to tabular, dark grey metallic crystals.

Named in 1827 from the Greek for "fire" and "to wash," because it was used to remove brown and green tints in the making of glass.