Erssonite, CaMg7Fe23+(OH)(18)(SO4)(2)center dot 12H(2)O, a new hydrotalcite-supergroup mineral from Långban, Sweden

• The new wermlandite-group mineral erssonite, ideally CaMg7Fe23+(OH)(18)(SO4)(2)center dot 12H(2)O (or [Mg7Fe23+(OH)(18)][Ca(SO4)(2)].12H(2)O), was discovered in a late-stage, low-temperature assemblage in cavities of a magnetite-bearing dolomitic rock from the Langban deposit, Varmland county, Bergslagen ore province, Sweden. The associated minerals are dolomite, calcite, members of the magnetite-magnesioferrite solid-solution series, phlogopite, chrysotile, pyroaurite and norbergite. Erssonite has a vitreous lustre and forms colourless, platy hexagonal crystals flattened on [0001], up to 0.5 mm across and up to 10 mu m thick, occurring mainly as aggregates in cavities of dolomitic rock. Erssonite is malleable; separate crystals are flexible and non-elastic, with a perfect, mica-like cleavage on {0001}. The calculated density is equal to 2.02 g.cm(-3). Raman spectroscopy shows the presence of typical bands for S-O bonds attributed to intercalated SO42- anions and structural OH- anions together with the absence of C-O bonds, attributed to carbonate anions. The chemical composition is (wt.%, electron microprobe, H2O content is calculated from structure data): MgO 28.67, CaO 2.76, Al2O3 0.23, Cr2O3 0.23, Fe2O3 16.00, SiO2 0.48, SO3 14.80, H2O 35.58, total 98.75. The empirical formula based on 38 O atoms is H41.48Ca0.52Mg7.47Fe2.113+Al0.05Cr0.03S1.94Si0.08O38. The ideal formula is CaMg7Fe23+(OH)(18)(SO4)(2).12H(2)O or {Mg7Fe23+(OH)(18)}{[Ca(H2O)(6)] (SO4)(2)(H2O)(6)}. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.093. Erssonite is trigonal, P (3) over bar c1, with a = 9.3550(6), c = 22.5462(14) angstrom, V = 1708.8(2) angstrom(3) and Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, angstrom (I, %)(hkl)] are: 11.22 (90)(002), 5.63 (64)(004), 4.670 (100)(110, 104, 014), 2.626 (64)(032, 302), 2.435 (66)(034, 304) and 1.951 (45)(038, 308). The mineral is named in honour of the Swedish amateur mineralogist Dr. Anders Ersson (b. 1971).

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

erssonite

new mineral

wermlandite group

hydrotalcite supergroup

crystal structure

IR spectroscopy

Raman spectroscopy

Langban mine

Bergslagen ore province

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