Abstract

A new magnesium borate found at Crestmore, California, has been named wightmanite, in honor of R. H. Wightman, Director of Exploration and Mining, Riverside Cement Company. It occurs as colorless, pseudohexagonal prisms, single or in radiating clusters, in a matrix of coarsely crystalline dolomite-calcite rock. Crystals are not terminated, but show {010}, {100} and {110) dominant. Two cleavages, {010} perfect and (100} fair, make an angle of 73° 30′. Difficultly soluble in cold dilute acids; G = 2.59; H = 5.5. Optically biaxial negative, with 2V = 33°; dispersion v>r strong; Z∧c=5°; α = 1.585, β = 1.603; γ =1.604.

Single crystal x-ray measurements show wightmanite to be triclinic pinacoidal, space group P1; a = 11.73 Å, b = 11.44 Å, c = 3.089 Å; α 96° 09′, β 97° 45½′, γ 105° 52½′. The powder pattern shows the following spacings and intensities of the strong lines: 10.70 (10), 9.07 (10), 3.03 (3), 2.67 (3).

Analysis: B2O3 12.2, MgO 57.8, CaO 2.7, FeO 2.2, A12O3 2.1, TiO2 0.16, H2O (+) 16.8, H2O (-) 4.7, Cl 0.94, F 1.8. Probable formula: 9MgO·B2O3·8H2O.

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