Maneckiite, ideally NaCa2Fe22+(Fe3+Mg)Mn-2(PO4)(6)(H2O)(2), a new phosphate mineral of the wicksite supergroup from the Michalkowa pegmatite, Gory Sowie Block, southwestern Poland

摘要

Maneckiite, ideally NaCa2Fe22+(Fe3+Mg)Mn-2(PO4)(6)(H2O)(2), was found in a pegmatite at Michalkowa, Gory Sowie Block, SW Poland. The mineral forms subhedral and anhedral crystals similar to 150 mu m x 150 mu m in the outer zone of phosphate nodules, where it is associated with fluorapatite, wolfeite, Ca-rich graftonite and alluaudite-group minerals. Maneckiite is transparent, dark brown, with a colourless streak and vitreous lustre, brittle, and has a good cleavage //{010}, a splintery fracture and a Mohs hardness of similar to 5. The calculated density is 3.531 g cm(-3). Maneckiite is pleochroic: alpha = dark green, beta = dark blue/green, gamma = light brown/tan, biaxial (+) with refractive indices alpha = 1.698(2), beta = 1.706(2), gamma = 1.727(2) and birefringence Delta = similar to 0.03; 2V(meas.) = 65.9 (1.5)degrees and 2V(calc.) = 64 degrees, dispersion is obscured by the dark colour, and optical orientation X//a, Y//b, Z//c. Maneckite is orthorhombic (Pcab) and has unit-cell parameters a = 12.526(4) angstrom, b = 12.914(5) angstrom, c = 11.664(4) angstrom and V = 1886.8(5) angstrom(3). The strongest reflections are (d(hkl) in angstrom; I; hkl): 2.759, 100, 402; 2.916, 78, 004; 3.020, 68, 401; 2.844, 35, 014; 2.869, 31, 240; 2.825, 30, 042. Maneckiite has the wicksite structure and is its Mn-M(3)-analogue. The mineral crystallized as a product of Na- and Ca-metasomatism induced by a HT fluid in the presence of Al3+ from a neighbouring aluminosilicate melt. A Gladstone-Dale index, 0.027, places maneckiite in the category 'excellent'.