What is Ramsdellite?
Ramsdellite is an orthorhombic manganese dioxide polymorph, usually dark and fine-grained, with importance in manganese-oxide mineralogy and ore deposits.
Mineralogy and crystal structure
Reference formula: MnO2. Ramsdellite is a polymorph of MnO2 and commonly intergrows with pyrolusite and other manganese oxides. Dark colour and dendritic texture alone do not establish the species. Ramsdellite is classified with oxides and has a orthorhombic crystal system. Typical hardness is 2–4 on the Mohs scale and specific gravity is approximately 4.7–5.0.
Colour, lustre and habit
Typical colours include black, dark grey, steel-grey, brown. The usual acicular, fibrous, massive habit and metallic, dull, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Ramsdellite forms in or is associated with supergene oxidation, weathering zones and manganese-rich hydrothermal or sedimentary deposits. Important documented localities include Greece, South Africa, India, Japan, Germany, Australia and the United States.
A dark polymorph in the manganese-oxide family
Ramsdellite is a useful guide mineral because it shows how the same chemical formula can support different crystal structures. Its commercial appeal is strongest in documented ore and polymorph collections.
Collecting and care
Avoid dust and acids, keep dry and preserve matrix. Do not grind or polish manganese-oxide material without appropriate controls.
