Abstract

Whiteite-(CaMgMg), CaMg3Al2(PO4)4(OH)2·8H2O, is a new mineral from the Northern Belle mine, Candelaria, Nevada, U.S.A. It is a low temperature, secondary mineral presumed to have formed as a result of hydrothermal alteration. It is associated with crandallite, fluorwavellite, montgomeryite, and variscite/metavariscite. The mineral occurs as colorless tapering blades, elongated parallel to [100], flattened on {001} and exhibiting the forms {100}, {010}, {001}, forumla, and forumla. The streak is white, the luster is vitreous, and crystals are transparent. The Mohs hardness is about 4. The tenacity is brittle, the fracture is irregular and stepped, and there is one perfect cleavage on {001}. The measured density is 2.48(1) g/cm3. The mineral is very slowly soluble in dilute HCl and slowly soluble in concentrated HCl. Whiteite-(CaMgMg) is biaxial (+), with α = 1.564(1), β = 1.565(1), γ = 1.575(1) (white light). The measured 2V is 24(1)°. No dispersion or pleochroism were observed. The optical orientation is X = b; Z ^ a = 41° in obtuse β. Electron-microprobe analyses gave the empirical formula Ca1.07Mg2.99Fe0.01Al1.91P4O26H18.11. The mineral is monoclinic, space group P2/a, with unit-cell parameters a 14.8237(19), b 7.0302(3), c 9.946(3) Å, β 110.115(12)°, V 973.3(3) Å3, and Z = 2. The five strongest lines in the X-ray powder diffraction patterns are [dobs Å(I)(hkl)]: 9.20(82)(001), 4.88(64)(210,forumla,111), 2.936(40)(401), 2.849(45)forumla, and 2.805(100)(022). The structure (R1 = 4.36% for 1401 reflections with Fo > 4σF) is the same as that of other jahnsite-group minerals.

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