Pyrolusite Identification Guide

What Pyrolusite Looks Like

Pyrolusite (MnO2) is the chief ore of manganese. It is iron-black to dark steel-gray, opaque, with a metallic to dull, sooty luster. Well-crystallized pyrolusite (rare, sometimes called the variety "polianite") shows prismatic tetragonal crystals, but most pyrolusite is massive, fibrous, radiating, columnar, granular, or powdery. It very commonly forms the black, tree-like dendrites seen on rock surfaces and inside agates, and soft, soiling crusts and coatings.

Step-by-Step Field ID Checklist

1. Note the color: iron-black to bluish steel-gray.
2. Check whether it soils your fingers: massive/powdery pyrolusite is sooty and marks the hands black.
3. Test hardness: typically very soft (1–2) when massive/earthy; well-crystallized polianite is harder (6–6.5). Most field specimens scratch easily.
4. Do the streak: black to bluish-black.
5. Look for form: dendrites, botryoidal crusts, radiating fibers, or compact masses.
6. Note associations: with other manganese oxides (romanèchite/psilomelane, manganite) and iron oxides in weathered/sedimentary settings.

Key Diagnostic Tests

• Streak: black to bluish-black — distinguishes it from hematite (red) and goethite/limonite (brown-yellow).
• Hardness: soft 1–2 massive (soils fingers); hard 6–6.5 only in crystalline polianite.
• Specific gravity: ~4.4–5.0.
• Luster: metallic in crystals, dull/earthy in masses.
• Habit: dendrites and botryoidal crusts are classic.
• No magnetism; reacts with hydrochloric acid releasing chlorine gas (do this only with care/ventilation).

Common Look-Alikes and How to Tell Them Apart

• Psilomelane/romanèchite: another black manganese oxide, but harder (5–6), hard and botryoidal, and does not soil the fingers as readily. Pyrolusite is softer and sootier.
• Manganite: brownish-black with a reddish-brown to black streak and better crystal form; pyrolusite's streak is purer black.
• Magnetite: black with a black streak too, but it is magnetic and harder (5.5–6.5) and does not soot.
• Hematite (specular/earthy): red to red-brown streak — the decisive difference.
• Graphite: also soft, black, and marks the fingers, but feels greasy and is much lighter (SG ~2.2) with a gray-black streak; pyrolusite is heavier and not greasy.

Where Pyrolusite Is Found

Pyrolusite forms under oxidizing conditions in bogs, lakes, and shallow marine sediments, and as a weathering product of other manganese minerals. Major deposits occur in Ukraine, Georgia, India, Brazil, South Africa, and Germany (Thuringia/Harz). Dendritic pyrolusite is found on countless limestone bedding planes and in 'dendritic' agates and 'landscape' stones worldwide.