RINMANITE, Zn2Sb2Mg2Fe4O14(OH)2, A NEW MINERAL SPECIES WITH A NOLANITE-TYPE STRUCTURE FROM THE GARPENBERG NORRA MINE, DALARNA, SWEDEN

Rinmanite, ideally Zn 2 Sb 2 Mg 2 Fe 4 O 14 (OH) 2 , is a new mineral species from the Garpenberg Norra Zn–Pb mine, Hedemora, Dalarna, in south-central Sweden, where it occurs in a skarn assemblage associated with tremolite, manganocummingtonite, talc, franklinite, barite and svabite. Rinmanite crystals are prismatic, up to 0.5 mm in length, with good {100} cleavage. The VHN 100 is in the range 841–907. D calc = 5.13(1) g·cm −3 . The mineral is black (translucent dark red in thin splinters) with a submetallic luster. The mineral is moderately anisotropic and optically uniaxial (−). Reflectance values measured in air are 13.5–12.1% (λ = 470 nm), 12.9–11.8% (546 nm), 12.6–11.7 (589 nm) and 12.2–11.3% (650 nm). Electron-microprobe analyses of rinmanite (wt.%) gave MgO 8.97, Al 2 O 3 0.82, MnO 2.47, Fe 2 O 3 34.33, ZnO 14.24, Sb 2 O 5 36.31, H 2 O 1.99 (calculated), sum 99.13, yielding the empirical formula (Zn 1.58 Mn 0.31 Mg 0.06 ) ∑1.95 Sb 2.03 [Mg 1.95 Fe 3.88 Al 0.15 ] ∑5.98 O 14.01 (OH) 1.99 . Rinmanite is hexagonal, space group P 6 3 mc , with a 5.9889(4), c 9.353(1) A, V 290.53(5) A 3 and Z = 1. A structure refinement from single-crystal Mo K α X-ray-diffraction data ( R = 3.1% for 199 reflections) shows that rinmanite is isostructural with nolanite. The octahedral M (1) and M (2) sites are occupied by (Mg + Fe) and Sb, respectively, whereas Zn is located at the 4-coordinated M (3) site. The strongest eight lines in the powder-diffraction pattern [ d in A ( I obs )( hkl )] are: 5.19(20)(100), 3.47(34)(102), 2.99(43)(110), 2.67(44)(103), 2.522(100)(112), 1.660(28)(213), 1.517(33)(205) and 1.497(54)(220). Mossbauer spectroscopy confirms that rinmanite contains Fe 3+ at octahedral sites and is in a paramagnetic state down to at least 77 K. Rinmanite is believed to have formed during prograde metamorphism of an initially low-S, siliceous carbonate protolith enriched in Zn, Sb and Fe, at relatively high P (H 2 O). The new mineral species is named after Sven Rinman (1720–1792), of Bergskollegium .