KRIVOVICHEVITE, Pb3[Al(OH)6](SO4)(OH), A NEW MINERAL SPECIES FROM THE LOVOZERO ALKALINE MASSIF, KOLA PENINSULA, RUSSIA

Abstract

Krivovichevite, Pb3[Al(OH)6](SO4)(OH), is a new sulfate found in a natrolite – aegirine – orthoclase vein within lujavrite at Mt. Lepkhe–Nelm, Lovozero alkaline massif, Kola Peninsula, Russia. It occurs as large (up to 1 cm diameter) equant grains within galena aggregates in natrolite, in intimate association with anglesite, cerussite, hydrocerussite, leadhillite and lanarkite. It is a late hydrothermal mineral produced by alteration of galena. Other associated minerals are anatase, arsenopyrite, fluorapatite, fluorite, halloysite, heulandite-Ca, heulandite-Sr, kupletskite, lamprophyllite, leucophanite, magnesio-arfvedsonite, mangan-neptunite, microcline, monazite-(La), polylithionite, quartz, opal, rhabdophane-(Ce) and titanite. The mineral is transparent and colorless, with a vitreous luster and a white streak. A cleavage was not observed, and the fracture is conchoidal. The Mohs hardness is about 3. The mineral is brittle. Krivovichevite is uniaxial (−): n (meas) ≈ 1.9 (589 nm), n (calc.) = 1.85. It is nonpleochroic. The mean chemical composition, determined with an electron microprobe is: PbO 76.49, CaO 0.02, Al2O3 5.38, SO3 9.27, H2O (Penfield method) 7.20, total 98.36 wt.%. The empirical formula, calculated on the basis of Pb + Ca + Al + S = 5 apfu is Pb3.04 Al0.94(S1.03O3.98)(OH)7.08. An ideal formula taking into account the single-crystal study of its structure is: Pb3[Al(OH)6](SO4) (OH). Krivovichevite is trigonal, R 3 c , a 7.693(8), c 31.57(9) A, V 1618(6) A3, Z = 6. The strongest six X-ray powder-diffraction lines [ d in A( I )( hkl )] are: 3.58(100)(201), 3.10(60)(116), 2.591(90)(119), 2.216(50)(030), 2.048(70)(036), 1.704(80)(317). The structure of krivovichevite has been refined to R 1 = 0.034 for 681 reflections. It contains isolated Al(OH)63− octahedra and SO42− tetrahedra, Pb2+ cations and OH− anions. The infrared spectrum indicates the presence of structural (OH)− and sulfate absorption bands. The mineral is named in honor of Sergey Vladimirovich Krivovichev, Russian mineralogist and crystallographer, Professor at St. Petersburg State University. Krivovichevite belongs to a new structure-type of minerals and inorganic compounds. Chemically related to krivovichevite are minerals of the beudantite and alunite groups.