Mangani-pargasite, NaCa2(Mg4Mn3+)(Si6Al2)O22(OH)2 , a new mineral species of the amphibole

Abstract

Mangani-pargasite, ideally NaCa 2 (Mg 4 Mn 3+ )(Si 6 Al 2 )O 22 (OH) 2 , is a new mineral species of the calcium amphibole subgroup of the amphibole supergroup. The type specimen was found on the mine dump of the Langban Fe-Mn-(Ba-As-Pb-Sb) deposit in Varmland, Bergslagen ore province, Sweden. Crystal chemical analyses resulted in the empirical chemical formula: A (Na 0.90 Pb 0.07 K 0.03 ) Σ1.00 B (Ca 1.93 Mn 2+ 0.07 ) Σ2.00 C (Mg 4.25 Mn 3+ 0.39 Al 0.26 Fe 3+ 0.10 ) Σ5.00 T (Si 6.35 Al 1.65 ) Σ8.00 O 22 W (OH) 2 . The mineral is biaxial positive, with a = 1.635(5), b = 1.645(5), c = 1.660(5) and the measured optic angle 2 V = 85(5)°. The dispersion is weak (r > v), and the optic orientation is: Y || b ; Z ^ c = 25(3)°. Mangani-pargasite is red to brownish red with weak pleochroism; X = pale reddish brown, Y = pale reddish brown and Z = pale brownish red; X ≈ Y > Z . The unit-cell parameters are a = 9.9448(5), b = 18.0171(9), c = 5.2829(3) A, b = 105.445(3)°, V = 912.39(9) A 3 , Z = 2, space group C 2/ m . The ten strongest reflections in the X-ray powder diffraction pattern [ d -values in A, I , ( h k l )] are: 8.420, 29, (1 1 0); 3.368, 17, (1 3 1), 3.279, 49, (2 4 0); 3.141, 100, (3 1 0); 2.817, 44, (3 3 0); 2.698, 21, (1 5 1); 2.389, 18, (3 5 0); 1.904, 29, (5 1 0); 1.650, 22, (4 6 1) and 1.448, 46, (6 6 -1).