Pyrolusite

Pyrolusite is manganese dioxide (MnO2) and the most important ore of manganese. Its name comes from Greek words meaning fire and to wash, because it was used to remove the green and brown tints from glass.

It commonly occurs as soft, sooty black masses, fibrous or columnar aggregates, and as the delicate branching black dendrites often seen on rock surfaces and in moss agate. Well-crystallized material (sometimes called polianite) is harder and more metallic.

Manganese from pyrolusite is essential to modern steelmaking, making this a mineral of major industrial value.

Pyrolusite forms under oxidizing, near-surface conditions. It precipitates from manganese-bearing waters in bogs, lakes, shallow marine basins, and in the oxidized zones of manganese ore deposits, where it can replace other manganese minerals such as rhodochrosite and manganite.

It also forms nodules and crusts on the deep ocean floor (manganese nodules) and produces the familiar dendritic coatings along rock fractures.

Major deposits occur in South Africa, Ukraine, Gabon, Australia, Brazil, and India, which together supply most of the world's manganese.

Look for a black to dark steel-gray mineral that is often soft and sooty, leaving a black mark on your fingers, with a black streak. Massive material can be very soft (around 2), while crystalline polianite is much harder.

Luster ranges from metallic in crystals to dull and earthy in massive forms. The dendritic, fern-like black growths on rock are a classic pyrolusite form.

Look-alikes include other black manganese oxides such as manganite and psilomelane (often harder, browner streak), and magnetite (magnetic). The black streak, frequent sootiness, and dendritic habit help identify pyrolusite.

Pyrolusite is the leading ore of manganese, a metal indispensable to steel production, where it removes impurities and increases strength and hardness. It is also used in aluminum alloys.

Beyond metallurgy, manganese dioxide from pyrolusite is used in dry-cell batteries, as a black and brown pigment, in glassmaking to decolorize or color glass, in ceramics, and as an oxidizer in chemical processes.

Collectors value crystalline specimens and attractive dendrites. It has no jewelry use, though dendritic rocks and moss-like patterns it creates are decorative. It has little metaphysical following.