Pyrolusite

Formula: Mn4+O2

Colour: Black or very dark grey.

Lustre: Metallic, Dull, Earthy

Hardness: 2 – 6½

Specific Gravity: 5.04 – 5.08

Crystal System: Tetragonal

Member of: Rutile Group

Name: 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.
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. May be confused with some manganese oxides such as todorokite (fibrous variants) and manganite (tabular crystals). No valid pyrolusite dendrites are known. Supposed specimens of pyrolusite in dendritic form turn out to be other Mn-oxide species (e.g., minerals of the cryptomelane group, birnessite, nsutite, todorokite, etc.) upon being examined in the proper laboratory setting for characterizing these difficult to identify minerals.