Psilomelane (Oxadized Manganiferous Siderite)

Here's a unique specimen, a mass featuring black, iridescent botryoids of psilomelane, this is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese oxide with variable amounts of barium and potassium. According to The Geological Survey of Canada, Bulletin 111 (1965), on the Geology, Geochemistry, and Origin of the Lead-Zinc-Silver Deposits of the Keno Hill-Galena Hill Area, Yukon Territory, "Next to limonite the hydrous manganese oxides are the most abundant supergene minerals in the vein faults and in fractures and faults in the rocks near the surface. X-ray determinations indicate that pyrolusite, psilomelane, and manganite are present in some samples, but generally the manganese oxides are so intimately inter-grown that they cannot be separated and determined. The term 'wad' best describes these mixtures and is used in this report. Most of the wad has resulted from the oxidation of manganiferous siderite. Small amounts may also have come from the alteration of sphalerite that contains up to 0.82 per cent Mn." This mineral assemblage is particularly noteworthy. This is an uncommon and visually striking example of psilomelane, not often encountered in collections.

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