The Tanic pegmatite at Bernic Lake, southeastern Manitoba. XV. Ercitite, NaMn3+PO4 (OH) (H2O)(2), a new phosphate mineral species

Ercitite, ideally Na Mn3+ (PO4) (OH) (H2O)(2), is a new mineral species fro m the Tanco pegmatite, southeastern Manitoba. Ercitite farms 200-400 mum ir regular aggregates of lath-like crystals in fan-like divergent sprays. The mineral occurs in a 5-cm nodule embedded in a quartz + spodumene pseudomorp h after petalite in the upper intermediate zone (5) of the pegmatite. The o uter rind of the nodule contains pink rhodochrosite, green and blue apatite , and minor yellow sphalerite, and the inner region is comprised of orange- brown lithiophilite. The core of the nodule consists of an assemblage of al tered lithiophilite, locally stained red (hematite?), colorless lithiophosp hate and dark brown-black clots of ercitite an collinsite, fairfieldite, wh itlockite and two unidentified phosphates; the new species and associated m inerals are alteration products of lithiophilite. Individual laths of ercit ite are light brown with a beige streak and a vitreous luster. Laths are ge nerally less than or equal to 20 mum across and less than or equal to 200 m um long, elongate along [(1) over bar 01] and flattened on {101}. Ercitite is brittle, with an irregular fracture on ends of laths, and has two very g ood orthogonal cleavages, parallel to{101} and {010}. Mohs hardness is 3-4, and the calculated density is 2.75 g/cm(3). Ercitite is biaxial positive, with alpha 1.699(2), beta 1.715(5), gamma 1.737(5), 2V(obs.) = 86 degrees, 2V(calc.) = 82 degrees, strongly pleochroic with X yellowish green, Y yello wish brown, Z very dark brown, with absorption Z >> Y > X and X = b, Y <^> c = 34 degrees (in beta acute), Z <^> a = 53 degrees (in beta obtuse). Erci tite is monoclinic, space group P2(1/n), a 5.362(5), b 19.89(1), c 5.362(5) Angstrom, beta 108.97(8)degrees V 540.8(6) Angstrom (3), Z = 4. The seven strongest lines in the X-ray powder-diffraction pattern [d(in Angstrom)(I)( h k l)] are: 9.90(10)(0 2 0), 2.644(8)(1 4 1), 3.273(6)(1 4(1) over bar), 3 .126( 6)(1 5 0, 0 5 1), 4.92(5)(0 1 1, 1 1 0), 2.542(4)(2 0 0, 0 0 2), 2.37 6(4)(1 7(1) over bar). Chemical analysis by electron microprobe gave P2O5 3 2.37, Al2O3 0.34, Mn2O3 18.81, Fe2O3 16.51, ZnO 0.08, MgO 0.12, CaO 1.09, N a2O 12.44, H2O (calc.) 20.44, sum 102.20 wt.% , where the valence states of Mn and Fe, and the amount of H2O, were determined by crystal-structure ana lysis. The resulting empirical formula on the basis of seven anions (includ ing OH and 2 H2O) is (Na0.89Ca0.04)(Sigma0.93) (Mn0.533+Fe0.463+Al0.01)(Sig ma1.00) (PO4)(1.01) (OH) (H2O)(2). Ercitite is structurally similar to berm anite, Mn2+ Mn-2(3+) (PO4)(2) (OH)(2) (H2O)(4) and is related by the substi tution 2Na --> Mn2+ + square (vacancy).