Ramsdellite Locality: Mistake Mine (Box Canyon deposits), Sam Powell Peak, Box Canyon District, Yavapai County , Arizona , USA ( Locality at mindat.org ) Size: 7.9 x 4.8 x 2.0 cm. In a pleasing sculptural vug is a plate of equant, splendent, black ramsdellite crystals, to .6 cm across. This is a superb example of the species, and a beautiful, 3-dimensional piece in person. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Ramsdellite
An orthorhombic manganese dioxide — one of the MnO₂ polymorphs of manganese deposits.
Intro adapted from Wikipedia (CC BY-SA).
Ramsdellite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MnO₂.
It crystallizes in the orthorhombic crystal system (space group Pnam). It is a member of the Ramsdellite structural group.
Key properties: Mohs hardness 3; specific gravity 4.65–4.83; Black, may have brownish tint streak; Brilliant metallic luster.
IMA symbol Rmd, grandfathered status — known before the IMA’s founding, named in 1932.
Found as a secondary mineral in manganese deposits, formed by inversion of pyrolusite or oxidative dehydrogenation of groutite.
It is found associated with Pyrolusite, hollandite, cryptomelane, coronadite.
The name refers to Professor Lewis Stephen Ramsdell (1895–1975), American mineralogist, University of Michigan, Ann Arbor, Michigan, USA.