Dritsite, Li 2 Al 4 (OH) 12 Cl 2 ·3H 2 O, a New Gibbsite-Based Hydrotalcite Supergroup Mineral

摘要

Dritsite, ideally Li 2 Al 4 (OH) 12 Cl 2 ·3H 2 O, is a new hydrotalcite supergroup mineral formed as a result of diagenesis in the halite?carnallite rock of the Verkhnekamskoe salt deposit, Perm Krai, Russia. Dritsite forms single lamellar or tabular hexagonal crystals up to 0.25 mm across. The mineral is transparent and colourless, with perfect cleavage on {001}. The chemical composition of dritsite (wt. %; by combination of electron microprobe and ICP?MS; H 2 O calculated by structure refinement) is: Li 2 O 6.6, Al 2 O 3 45.42, SiO 2 0.11, Cl 14.33, SO 3 0.21, H 2 O calc. 34.86, O = Cl ? 3.24, total 98.29. The empirical formula based on Li + Al + Si = 6 apfu (atom per formula unit) is Li 1.99 Al 4.00 Si 0.01 [(OH) 12.19 Cl 1.82 (SO 4 ) 0.01 ] Σ14.02 ·2.60(H 2 O). The Raman spectroscopic data indicate the presence of O–H bonding in the mineral, whereas CO 3 2– groups are absent. The crystal structure has been refined in the space group P 6 3 / mcm , a = 5.0960(3), c = 15.3578(13) ?, and V = 345.4(5) ? 3 , to R 1 = 0.088 using single-crystal data. The strongest lines of the powder X-ray diffraction pattern ( d , ? ( I , %) ( hkl )) are: 7.68 (100) (002), 4.422 (61) (010), 3.832 (99) (004, 012), 2.561 (30) (006), 2.283 (25) (113), and 1.445 (26) (032). Dritsite was found as 2 H polytype, which is isotypic with synthetic material and shows strong similarity to chlormagalumite-2 H . The mineral is named in honour of the Russian crystallographer and mineralogist Prof. Victor Anatol`evich Drits.