Introducing the akrochordite mineral group, with the new mineral vargite from the Långban Mn-Fe deposit, Filipstad, Värmland, Sweden
收藏DataCite Commons2025-07-02 更新2025-05-07 收录
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资源简介：
Vargite, ideally MnCu<sub>2</sub>Mn<sub>2</sub>(OH)<sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>(AsO<sub>4</sub>)<sub>2</sub> – named after the Swedish miner Erik Gustaf Varg (1886–1970), who collected the type specimen – was found in the Långban Fe-Mn deposit. It occurs in open cavities in a brecciated and later hydrothermally leached carbonate groundmass, in association with hausmannite, calcite, rhodochrosite, baryte, a serpentine-group mineral, and galena. Additional minor phases are hedyphane, phlogopite and yarrowite. Paragenetically, it is a late-stage mineral, formed as a result of the interaction between an As-rich hydrothermal fluid and Mn-oxide(s) and Cu-sulphide, under low <i>P</i>- and <i>T</i>-conditions. Vargite forms bright green, semi-spherical aggregates up to 0.5 mm across, consisting of numerous thin, lath-shaped crystals, elongated along [100] and with a maximum length of 200 µm. Mohs hardness is ≈ 3 and <i>D</i><sub>calc </sub>= 3.49(1) g·cm<sup>−3</sup>. The empirical chemical formula obtained from electron probe micro-analyses analyses and based on 16 anions is (Cu<sub>1.77</sub>Mg<sub>0.33</sub>)<sub>Σ2.10</sub>(Mn<sub>2.94</sub>Ca<sub>0.04</sub>Pb<sub>0.01</sub>)<sub>Σ2.99</sub>(As<sub>1.95</sub>Si<sub>0.02</sub>)<sub>Σ1.97</sub>O<sub>8</sub>(OH)<sub>4.03</sub>·3.98H<sub>2</sub>O. The crystal structures of vargite and the isotypic mineral akrochordite [MnMn<sub>2</sub>Mn<sub>2</sub>(OH)<sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>(AsO<sub>4</sub>)<sub>2</sub>] have been refined in the space group <i>P</i>2<sub>1</sub>/<i>c</i> from single-crystal X-ray diffraction data to <i>R</i>1 = 3.07% and 2.46%, respectively, giving the following sets of unit-cell parameters: <i>a</i> = 5.6251(14), 5.6832(11) Å, <i>b =</i> 17.452(5), 17.631(5) Å, <i>c</i> = 6.905(2), 6.8417(19) Å, β = 100.21(5)°, 99.51(4)°, and <i>V</i> = 667.2(3), 676.1(3) Å<sup>3</sup>, with Z = 2. A Raman spectrum of vargite, with major bands at 3510, 1610, 850, 780, 476, 428, 389, and 308 cm<sup>−1</sup>, strongly resembles that of isotypic guanacoite, [MgCu<sub>2</sub>Mg<sub>2</sub>(OH)<sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>(AsO<sub>4</sub>)<sub>2</sub>]. Vargite, akrochordite, and guanacoite constitute the newly established akrochordite group.
提供机构：
Taylor & Francis
创建时间：
2025-01-22
