A new borosilicate mineral, werdingite, is reported from the granulite facies of the Namaqualand metamorphic complex at Bok se Puts, Namaqualand, South Africa. The mineral occurs in association with komerupine and grandidierite in a sillimanite-hercy-nite-rich band in a supracrustal gneissic sequence. It has the chemical composition MgO 4.46, FeO 5.06, Al2O3 59.49, TiO2 0.05, SiO2 19.83, B2O3 10.19, sum 99.08 wt%. This corresponds to the ideal formula (Mg,Fe)2Al14Si4B4O37. The unit cell of werdingite is triclinic, space group P1, with a = 7.995(2), b = 8.152(1), c = 11.406(4) Å, α = 110.45(2)°, β = 110.85(2)°, γ = 84.66(2)°, V= 650.5(3) Å3, and Z = 1. The X-ray powder-diffraction lines with the strongest intensities are [d(Å), I, hkl] 5.43(80)(110), 5.23(100)(110), 4.98(75)(002,112), 3.392(50)(210); 2.708(60)(220), 2.194(50)(2l4,034), and 1.527(40)(244,424). Werdingite is brownish yellow and translucent with a vitreous luster, conchoidal fracture, and Mohs’ hardness of 7. It has a measured density of 3.04 g/cm3, and a calculated value of 3.07 g/cm3, and it occurs as anhedral to subhedral xenoblasts up to 3 mm in diameter. The optical properties of werdingite include biaxial (—); 2V= 33(1)° (meas.), 42°(calc.); α = 1.614(2), β = 1.646(2), γ = 1.651(2); strong dispersion, r > ν; Z = c; pleochroism, X, Z colorless and Y yellow. Werdingite is named in honor of Dr. Günter Werding, Institut für Mineralogie, Ruhr-Universität, Bochum, Germany.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.