MALEEVITE, BAB2SI2O8, AND PEKOVITE, SRB2SI2O8, NEW MINERAL SPECIES FROM THE DARA-I-PIOZ ALKALINE MASSIF, NORTHERN TAJIKISTAN: DESCRIPTION AND CRYSTAL STRUCTURE

Abstract

Maleevite, ideally Ba B-2 Si-2 O-8, and pekovite, ideally Sr B-2 Si-2 O-8, are two new mineral species found in boulders in the moraine of the Dara-i-Pioz glacier, the Alai range, Tien Shan, Garmskii district, northern Tajikistan. Both minerals occur as anhedral equant crystals from 0.5 to 2 mm in diameter. Crystals of both minerals are white to transparent with a white streak and a vitreous luster. Maleevite occurs in aegirine - microcline - quartz pegmatite in syenites with arfvedsonite, polylithionite, reedmergnerite, cesium-kupletskite, hyalotekite, albite, dusmatovite, pyrochlore, tadzhikite, tienshanite, sogdianite, stillwellite-(Ce), leucosphenite, leucophanite, willemite, danburite, zektzerite, berezanskite, baotite, cappelenite-(Y) and an unknown Y-Ca silicate. Pekovite Occurs in a rock consisting mainly of quartz with subordinate pectolite, aegirine, stillwellite-(Ce), polylithionite, leucosphenite and reedmergnerite. More rarely, turkestanite, galena, calcite, kapitsaite-(Y), neptunite, sugilite, baratovite, bismuth, sphalerite, fluorite, pyrochlore, fluorapatite, and zeravshanite occur in the same rock. Pekovite commonly forms intergrowths with pectolite, quartz, strontian fluorite and aegirine. Maleevite fluoresces intense blue in short-wave ultraviolet light. Malleevite and pekovite show no cleavage, have a Mobs hardness of 7, and are brittle with uneven fracture. The observed and calculated densities are as follows: maleevite, D(obs.) = 3.78(1), D(calc.) = 3.79; pekovite, D(obs.) = 3.35(2), D(calc.) = 3.36 g/cm(3).