Abstract
The chemical composition of romeite from the regionally metamorphosed bedded manganese ore deposit of the Gozaisho mine, Fukushima Prefecture, is (Na1.00Ca0.80Mn0.01)Σ1.81Sb2 [O5.69F0.89(OH)0.36]Σ6.94, calculated on the basis of Sb=2. It occurs as honey yellow to brownish yellow octahedra up to 4 mm long in braunite-rhodonite ore. It is cubic, Fd3m, a=10.265(2) Å, Z=8. Microbalance measured specific gravity is close to the calculated density 5.096 g/cm3. The single crystal study using the four-circle diffractometer confirms the isostructural relation to pyrochlore and stibiconite group minerals, yielding R=1.3%; Rw=1.8%. The precise ideal formula of romeite is to be simply NaCaSb2O6(F, OH). The quantitative relation of Na to Ca is similar to the case of pyrochlore series minerals where Ca≥Na.
