Qingheiite-(Fe2+), Na2Fe2+MgAl(PO 4)3, a new phosphate mineral from the Sebastião Cristino pegmatite, Minas Gerais, Brazil

Frédéric Hatert, Maxime Baijot, Simon Philippo, Johan Wouters

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Qingheiite-(Fe2+), ideally Na2Fe 2+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 A = 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, Al2O 3 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 (□0.65Na0.35)Σ1.00(Na 0.58Mn2+ 0.40Cao.o2)z;i.oo (Fe2+ 0.68Mn2+ 0.32)Σ1.00 (Mg 0.72Fe3+ 0.23Fe2+ 0.05) Σ1.00(Al0.62Fe3+ 0.38) Σ1.00[PO4]3. The single-crystal unit-cell parameters are a = 11.910(2), b = 12.383(3), c = 6.372(1) Å, β = 114.43(3)°, and V= 855.6(3) Å3, space group P2 1/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.

langue originaleAnglais
Pages (de - à)459-467
Nombre de pages9
journalEuropean Journal of Mineralogy
Numéro de publication3
Les DOIs
Etat de la publicationPublié - 1 mai 2010

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