• Wouters, Johan
• Baijot, Maxime
• Philippo, Simon
• Hatert, Frédéric

Abstract

<p>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 &gt; 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 (□_0.65Na_0.35)_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(Al_0.62Fe³⁺ _0.38) Σ_1.00[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) ų, 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.</p>

Topics

• density
• impedance spectroscopy
• mineral
• dispersion
• grain
• hardness
• powder X-ray diffraction
• space group