Steklite, KAl(SO4)2: A finding at the Tolbachik Volcano, Kamchatka, Russia, validating its status as a mineral species and crystal structure

Abstract

Steklite KAl(SO4)2 has been found in sublimates of the Yadovitaya (Poisonous) fumarole at the second cinder cone of the northern breach of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. Steklite was approved as a valid mineral species by the Commission on New Minerals, Nomenclature, and Mineral Classification of the International Mineralogical Association on June 2, 2011 (IMA no. 2011-041). The name steklite is left for this mineral, as it was named by Chesnokov et al. (1995) for its technogenic analog from a burnt dump of coal mine no. 47 at Kopeisk, the Southern Urals, Russia. It is named after the Russian word steklo, meaning glass, in allusion to the visual similarity of its lamellae to thin glass platelets. At Tolbachik, steklite is associated with alumoklyuchevskite, langbeinite, euchlorine, fedotovite, chalcocyanite, hematite, and lyonsite. It occurs as hexagonal or irregular-shaped lamellar crystals with the major form {001} reaching 30 μm in thickness and 0.2 mm (occasionally up to 1 mm) in width. The crystals are frequently split. They are combined into openwork aggregates or thin crusts up to 1.5 × 2.5 cm in area. Steklite is transparent and colorless, with vitreous luster. The cleavage is perfect, parallel to (001). The mineral is brittle. The Mohs’ hardness is 2.5. D calc is 2.797 g/cm3. Steklite is optically uniaxial, (−), ω = 1.546(2), ɛ = 1.533(3). The chemical composition (wt %, electron-microprobe data) is as follows: 0.09 Na2O, 18.12 K2O, 0.08 CaO, 0.03 MnO, 2.02 Fe2O3, 18.18 Al2O3, 61.80 SO3. The total is 100.37. The empirical formula calculated on the basis of eight O atoms is: (K0.997Na0.008Ca0.004)Σ1.009(Al0.925Fe 0.066 3+ Mg0.003Mn0.001)Σ0.995S2.01O8. Steklite is trigonal, space group P321, a = 4.7281(3), c = 7.9936(5) A, V = 154.76(17)A3, Z =1. The strongest reflections in the X-ray powder diffraction pattern (d, A-I[hkl]) are: 8.02–34[001], 4.085–11[100], 3.649–100[011, 101], 2.861–51[012, 102], 2.660 - 19[003], 2.364–25[110], 2.267–14[111, 111, 103], 1.822–12[022, 202]. In the structure of steklite examined in microtwinned crystal with R = 0.0732, the SO4 tetrahedral anions are shared-corners with distorted AlO6 trigonal prisms to form ∞ 2 [(Al, Fe) (SO4)2]− layers coplanar to (001). The K+ cations are in the interlayer space. The type specimen of steklite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.