Abstract

Headden's unnamed sodium iron manganese phosphate from the Nickel Plate pegmatite, S. Dak., has been reexamined and its identity with arrojadite from the Serra Branca pegmatite, Brazil, has been established by direct comparison. The optical properties of arrojadite from the Nickel Plate pegmatite are: α = 1.664, β = 1.670, and γ = 1.675; X colorless, Y pale green, Z pale yellow green, X = b, Za = 18°, 2V=86°, r<v strong. New optical properties of arroj′adite from other localities are given. The space group is C2/m. (C32h) and the unit cell has a0= 16.60, b0 = 10.02, and c0 = 23.99 Å; a:b:c = 1.656:1:2.389, β=93° 37′.

Material from Hiihnerkobel, Bavaria, and from Norro, Sweden, originally described as arrojadite is not isostructural with arrojadite from the Nickel Plate pegmatite and from the Serra Branca pegmatite, and the name hiihnerkobelite is proposed for this partly oxidized material with formula (Na2, Ca)O · 2(Fe, Mn)O · P2O5.

Graftonite (Fe, Mn, Ca)3(PO4)2 is associated with arrojadite at the Nickel Plate pegmatite. A new analysis is given, together with a partial analysis of graftonite from the Rice pegmatite, and optical properties are correlated with chemical composition. Optical properties of the graftonite from the Nickel Plate pegmatite are: α=1.709, β = 1.714, γ = 1.736, X colorless, Y colorless, Z pink, X=b, Z⋀c=36°, 2V=53°, biaxial+, r<v strong. The space group is P2i/c(C62h); the unit cell has a0=8.87, b0=11.57, and c0=6.17 Å; a:b:c = .766:1:.533, β = 99°12′. The relationship between the new cell and the Penfield orientation is discussed.

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