Mbobo Mkulu Cave, South Africa - mineral species not aproved by IMA-CNMNC
Speleothems: Nodules
Frequency: Extremely Rare
Other geologic settings: The cave is developed at the contact between a thick layer of Archean dolomite and an overlying chert breccia (which forms the ceiling of nearly all the rooms and passages of the cave) The breccia represents the siliceous residue after karst dissolution of dolomite, and it is overlain in places by thin quartzite and by a continous black shale (with disseminated sulfides)
Location within cave: Third chamber of the cave, forming mounds on the floor
First description of cave occurrence: Martini, J.E.J. 1980. Mbobomkulite, hydrombobomkulite and nickelaluminite, new minerals from Mbobo Mkulu Cave, Eastern Transvaal. Annals of the Geological Survey of South Africa 14(2): 1-10
First description of non-cave occurrence: -
Dolomite
Age: Precambrian
Chemical formula:
[According to the official IMA-CNMNC List of Mineral Names (http://nrmima.nrm.se/imalist.htm)]
Deposition and stability: Product of oxidation and leaching of Ni-Cu from sulfides in the cave roof, reacting with aluminum and potassium from phyllosilicates in shale matrix, and nitrate from bat guano.
Luster: Dull
Hardness: Low (not measured)
Cleavage: Perfect {001}
Electron microprobe, X-ray powder diffraction, optical properties
Chemical analysis: Electron microprobe.
Mineral assemblage: Associated with allophane
Cell parameter b (Å): 8,860
Cell parameter c (Å): 17,174
Cell parameter α (Å): 1,532
Cell parameter β (Å): 95,95
Cell parameter γ (Å): 1,543
Crystal size: Sub-millimeter finely grained crystals
Pseudohexagonal thin plates (10 um, across), pilling up along the c axis, forming rosettes.