• journal_title：Mineralogical Magazine
• Contributor：E. V. Galuskin ; I. O. Galuskina ; V. M. Gazeev ; P. Dzierżanowski ; K. Prusik ; N. N. Pertsev ; A. E. Zadov ; R. Bailau ; A. G. Gurbanov
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2011.075.5.2563
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：75
• issue：5
• firstpage：2563
• section：Articles

Megawite is a perovskite-group mineral with an ideal formula CaSnO₃ that was discovered in altered silicate-carbonate xenoliths in the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia. Megawite occurs in ignimbrite, where it forms by contact metamorphism at a temperature >800°C and low pressure. The name megawite honours the British crystallographer Helen Dick Megaw (1907–2002) who did pioneering research on perovskite-group minerals. Megawite is associated with spurrite, reinhardbraunsite, rondorfite, wadalite, srebrodolskite, lakargiite, perovskite, kerimasite, elbrusite-(Zr), periclase, hydroxylellestadite, hydrogrossular, ettringite-group minerals, afwillite, hydrocalumite and brucite. Megawite forms pale yellow or colourless crystals up to 15 μm on edge with pseudo-cubic and pseudo-cuboctahedral habits. The calculated density and average refractive index are 5.06 g cm⁻³ and 1.89, respectively. Megawite is Zr-rich and usually crystallizes on lakargiite, CaZrO₃. The main bands in the Raman spectrum of megawite are at: 159, 183, 262, 283, 355, 443, 474, 557 and 705 cm⁻¹. The unit-cell parameters and space group of megawite, derived from electron back scattered diffraction, are: m>am> = 5.555(3), m>bm> = 5.708(2), m>cm> = 7.939(5) Å, m>Vm> = 251.8(1) ų, m>Pbnmm>, m>Zm> = 4; they are based on an orthorhombic structural model for the synthetic perovskite CaSn_0.6Zr_0.4O₃.