What is Oxycalcioroméite?
Oxycalcioroméite is a rare cubic antimony oxide of the roméite group, typically found in oxidised manganese and antimony deposits.
Mineralogy and crystal structure
Reference formula: Ca2Sb2O7. The roméite group has a pyrochlore-related framework with extensive substitutions. The ideal formula is a simplified end-member expression and natural material may contain fluorine, titanium and other elements. Oxycalcioroméite is classified with oxides and has a cubic crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 5.0–5.5.
Colour, lustre and habit
Typical colours include yellow, brown, black, green. The usual octahedral, cubic, massive habit and vitreous, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Oxycalcioroméite forms in or is associated with oxidised antimony-bearing manganese deposits and complex hydrothermal ore zones. Important documented localities include Italy, France, Germany, Australia, Mexico and South Africa.
A cubic oxide from a manganese cap
Oxycalcioroméite turns a complex ore assemblage into a precise structural motif. Its cubic framework belongs to a family where small substitutions create a wide range of dark and colourful oxides.
Collecting and care
Keep dry and avoid dust; do not grind or use in jewellery, and wash hands after handling antimony-bearing minerals.
