Qingheiite-(Fe⁺), Na₂Fe²⁺MgAl(PO₄)₃, a new phosphate mineral from the Sebastião Cristino pegmatite, Minas Gerais, Brazil

Authors: Hatert, Frédéric; Baijot, Maxime; Philippo, Simon; Wouters, Johan

Source: European Journal of Mineralogy, Volume 22, Number 3, June 2010 , pp. 459-467(9)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

Qingheiite-(Fe²⁺), ideally Na₂Fe²⁺MgAl(PO₄)₃, is a new mineral species from the Sebastião Cristino pegmatite, Minas Gerais, Brazil. It occurs as rims around frondelite grains, included in a matrix of quartz and albite. Frondelite is locally replaced by jahnsite, cyrilovite and Fe-Mn oxides. Qingheiite-(Fe²⁺) is transparent and exhibits a dark green colour, with a resinous lustre and with a pale to bottle green streak. It is non-fluorescent, brittle, and shows a perfect {010} cleavage. The estimated Mohs hardness is 4. The measured density is 3.6(2) g/cm³; the calculated density is 3.54 g/cm³. Qingheiite-(Fe²⁺) is biaxial negative, with α = 1.692(5), β = 1.718(3), and γ = 1.720(5) (with λ = 590 nm). Pleochroism is from pale pinkish brown (X) to pale green (Y) and pale bluish grey (Z). The calculated 2V angle is 31°, and a strong dispersion r > v has been observed. The β index is parallel to the b crystallographic axis; α and γ lie in the (010) plane. Electron microprobe analyses gave P₂O₅ 46.51, Al₂O₃ 6.94, Fe₂O₃ 10.58, FeO 11.46, MgO 6.32, MnO 11.23, CaO 0.24, Na₂O 6.27, K₂O 0.01, total 99.56 wt. %. The resulting empirical formula, calculated on the basis of 3 P, is (□_0.65Na_0.35)_Σ1.00(Na_0.58Mn²⁺_0.40Ca_0.02)_Σ1.00 (Fe²⁺_0.68Mn²⁺_0.32)_Σ1.00 (Mg_0.72Fe³⁺_0.23Fe²⁺_0.05)_Σ1.00(Al_0.62Fe³⁺_0.38)_Σ1.00[PO₄]₃. The single-crystal unit-cell parameters are α = 11.910(2), β = 12.383(3), c = 6.372(1) Å, β = 114.43(3)°, and V = 855.6(3) Å³, space group P2₁/n. The eight strongest lines in the powder X-ray diffraction pattern [d(in Å)(I)(hkl)] are: 3.468(35)(310), 3.047(100) (112), 2.849(80) (312), 2.810(35) (222), 2.711(40)(330), 2.688(90)(240), 2.500(40) (132; 112), 2.074(30) (313). Qingheiite-(Fe²⁺) is the Fe²⁺ analogue of qingheiite, and belongs to the wyllieite group of minerals. The crystal structure has been refined, based on single-crystal X-ray diffraction data, to R₁ = 2.91%. The mineral species and name were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (CNMNC-IMA) under number 2009-076.

Keywords: QINGHEIITE-(FE2+); NEW MINERAL; PHOSPHATE; WYLLIEITE GROUP; MINAS GERAIS; BRAZIL

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2010/0022-2030

Publication date: 2010-06-01

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