Ramsdellite
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| Ramsdellite | |
|---|---|
 Sample from Mistake Mine, Box Canyon District, Yavapai County, Arizona, USA | |
| General | |
| Category | Oxide minerals |
| Formula | MnO2 |
| IMA symbol | Rmd[1] |
| Strunz classification | 04.DB.15a |
| Dana classification | 04.04.07.01 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal |
| Space group | Pbnm (no. 62) |
| Identification | |
| Formula mass | 86.94 gm (Mn 63.19% O 36.81%) |
| Color | Iron black, Black, Steel gray |
| Crystal habit | Granular / Massive-Fibrous / Platy |
| Cleavage | Good |
| Fracture | Conchoidal to uneven[2] |
| Tenacity | Brittle |
| Mohs scale hardness | 3 – Calcite |
| Luster | Metallic |
| Streak | Brownish black |
| Diaphaneity | Opaque |
| Specific gravity | 4.79 g/cm3 (calculated) |
| Density | 4.37 g/cm3 (measured) |
| Optical properties | NCalc= 2.89 (Dcalc) / 2.72 (Dmeas) |
| References | [3] |
Ramsdellite (Mn4+O2) is an orthorhombic manganese dioxide mineral. It is relatively uncommon, and is usually found in deposits containing other manganese oxide crystals.
Ramsdellite is named after the American mineralogist, Lewis Stephen Ramsdell (1895–1975).[3] Ramsdell spent almost all his career at the University of Michigan as a professional mineralogist. Ramsdellite was one of the new phases he first recognized in the "black manganese oxide" minerals. It was later named in his honour by Michael Fleischer and W. E. Richmond, who fully described the mineral in 1943.[4] The mineral is also called Groutellite.[5]
Chemistry and crystallography
The chemical formula for Ramsdellite is MnO2. The empirical formula is Mn4+O2.[3] Ramsdellite has the same chemistry as the more common pyrolusite, but is orthorhombic where pyrolusite is tetragonal.[2] Ramsdellite belongs to the Orthorhombic crystal system and Dipyramidal crystal class.[5] Properties:[6]
| Crystal | System | Orthorhombic |
| Point group | 2/m 2/m 2/m | |
| Form | Often pseudomorphs of groutite crystals | |
| Crystal habit | Platy, fibrous or massive | |
| Physical | Cleavage | Prominent, on three pinacoids and a prism |
| Tenacity | Brittle | |
| Hardness (Mohs scale) | About 3 | |
| D | Measured = 4.65–4.83 Calculated = 4.84 | |
| Optical | Opaque | |
| Color | Steel-gray to iron-black; yellowish white in reflected light. | |
| Streak | Black, may have brownish tint | |
| Luster | Brilliant metallic. | |
| Optical Class | Biaxial | |
| Anisotropism | Strong; pale yellow | |
| Bireflectance | Distinct. | |
| Cell | Space group | Pbnm. a = 4.533(5) b = 9.27(1) c = 2.866(5) Z = 4 |
Classification
The Dana classification is 4.4.7.1 (simple oxides: AX2). The Hey's CIM Ref is 7.18.8 (Oxides and Hydroxides, Oxides of Mn).[5] The Nickel–Strunz classification is 04.DB.15a, since the metal:oxygen ratio is around 1:2 and the mineral has medium-sized cations; chains of edge-sharing octahedra.[3] Other elements in the Ramsdellite / 04.DB.15 group are Paramontroseite: V4+O2 (15a), Akhtenskite: ε-Mn4+O2 (15b) and Nsutite: (Mn4+,Mn2+)(O,OH)2 (15c).[7][5]
