Calcium and Magnesium-bearing Sabugalite from the Tono Uranium Deposit, Central Japan

摘要

Calcium and magnesium-bearing sabugalite occurs as aggregations of yellowish platy crystals in veinlets or druses in conglomerate from the oxidized parts of the Tono uranium deposit, Central Japan. X-ray powder diffractometry of this mineral has reflections consistent with previous powder diffraction data of sabugalite. It is included in the monoclinic system with space group C2/m and calculated cell parameters of a = 19.68A, b = 9.89A, c = 9.82A α = γ = 90°, β=96.93° and V = 1897.83A~3. Chemical analysis yields a formula of (Ca_(0.10)Mg_(0.09))_(Σ0.19)Al_(0.53)(UO_2)_(2.04)((PO_4)_(1.99)(AsO_4)_(0.01))_(Σ2.00)-11.22H_2O. EMPA mapping shows that the mineral is com-positionally uniform with no micron-scale layering. Charge of cations including Ca and Mg in the cation-H2O layer is 1.98 being identical to that of autunite group minerals. This suggests that the charge balance in the cation-H_2O layer of the mineral could be made by the alkaline earth or alkaline elements rather than by hydrogen ions.