Beusite-(Ca), ideally CaMn22 (PO4)2, a new graftonite-group mineral from the Yellowknife pegmatite field, Northwest Territories, Canada: Description and crystal structure
Hawthorne, Frank C., Wise, Michael A., Cerný, Petr, Abdu, Yassir A., Ball, Neil A., Pieczka, Adam, and Wlodek, Adam. 2018. "Beusite-(Ca), ideally CaMn22 (PO4)2, a new graftonite-group mineral from the Yellowknife pegmatite field, Northwest Territories, Canada: Description and crystal structure." Mineralogical Magazine, 82, (6) 1323–1332. https://doi.org/10.1180/mgm.2018.120.
Beusite-(Ca), ideally Ca (PO4)2, is a new graftonite-group mineral from the Yellowknife pegmatite field, Northwest Territories, Canada. It occurs in a beryl-columbite-phosphate rare-element pegmatite where it is commonly intergrown with triphylite-lithiophilite or sarcopside, and may form by exsolution from a high-temperature (Li,Ca)-rich graftonite-like parent phase. It occurs as pale-brown lamellae 0.1-1.5 mm wide in triphylite, and is pale brown with a vitreous lustre and a very pale-brown streak. It is brittle, has a Mohs hardness of 5, and the calculated density is 3.610 g/cm3. Beusite-(Ca) is colourless in plane-polarized light, and is biaxial ( ) with ? = 1.685(2), ? = 1.688(2), ? = 1.700(5), and the optic axial angle is 46.0(5)°. It is non-pleochroic with X || b; Y ? a = 40.3° in ? obtuse; Z ? a = 49.7° in ? acute. Beusite-(Ca) is monoclinic, has space group P21/c, a = 8.799(2), b = 11.724(2), c = 6.170(1) Å, ? = 99.23(3)°, V = 628.3(1) Å3 and Z = 4. Chemical analysis by electron microprobe gave P2O5 41.63, FeO 19.43, MnO 23.63, CaO 15.45, sum 100.14 wt.%. The empirical formula was normalized on the basis of 8 anions pfu: (Ca0.94Fe0.92Mn1.13)?2.99(PO4)2.00. The crystal structure was refined to an R1 index of 1.55%. Beusite-(Ca) is a member of the graftonite group with Ca completely ordered at the [8]-coordinated M(1) site.
