Psilomelane: The trick is in the cutting

Psilomelane is a mineral name that is losing its significance. Still in use around the world the name is applied to hydrated barium bearing manganese specimens. Psilomelane is probably a mixture of several minerals but is composed mostly of the mineral Romanechite. The difficulty in distinguishing romanechite from other barium manganese oxides, that are probably mixed together in the same specimen, is why the name psilomelane is still in use. Psilomelane, more rare than pyrolusiteis is still an important ore of manganese. Manganese is a strategically valuable metal since it is an essential ingredient in steel and other alloys. The mining term "wad" is used to indicate ores that are a mixture of several manganese oxides such as psilomelane, pyrolusite and others that are difficult to distinguish. Psilomelane is often banded with gray pyrolusite and the alternating layers make an attractive polished stone with bands of metallic gray and submetallic black. Psilomelane also forms tufts of hair-like aggregates that are similar to those produced by pyrolusite. However, the difference in luster between the two minerals is usually sufficient to distinguish them. Pyrolusite is also soft enough to leave marks on fingers and paper.

Cutting Psilomelane:

Contrary to normal lapidary cutting procedures and due to the hardness and nature of psilomelane we recommend following this advice when cutting. We have found that the largest, thickest blade at the SLOWEST possible feed rate provides the best cut. This pattern is what makes this material famous. Keep material cool and wet when grinding as it can be a bit heat sensitive. We use tin oxide on a leather buff to put a final polish on this material.

Physical Characteristics:

• Chemical Formula: Barium Manganese Oxide Hydroxide (H4MnO6)
• Hardness: 5 - 5.5.
• Specific Gravity: 4.4 - 4.5 (heavy for non-metallic minerals)
• Class: Oxides and Hydroxides.
• Uses: An ore of manganese and as a mineral specimen.
• Color: Variable from iron-black to bluish black to steel gray.
• Luster: Submetallic to dull in earthy specimens.
• Transparency: Crystals are opaque.
• Crystal System: Monoclinic.
• Cleavage: Absent.
• Other Properties: Sometimes banded with the mineral pyrolusite producing alternating bands of metallic gray and submetallic black.
• Associated Minerals: Hematite, quartz, pyrolusite and other manganese oxide minerals.
• Sources: Austinville, Wythe County, Virginia, Upper Peninsula of Michigan and Tucson, Arizona, USA; Schneeburg, Germany; Cornwall, England; Ouro Preto, Minas Gerias, Brazil and elsewhere.

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Last modified: November 20, 2009