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Formula: CaSnO3
Oxide, perovskite subgroup,
stoichiometric perovskites group,
perovskite supergroup,
tin-bearing mineral, forms series with
perovskite and lakargiite
Crystal System: Orthorhombic
Specific gravity: 5.06 calculated
Streak: White
Colour: Pale yellowish brown, pale yellow to colourless
Environments
Megawite was approved in 2010 but to date (June 2025) it has been reported only from the Lakargi Mountain.
Localities
The type locality is Xenolith no. 3, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District,
Kabardino-Balkaria, Russia.
At Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District, Kabardino-Balkaria, Russia,
crystals of zirconium-bearing megawite were found in the
spurrite zones of the skarned
xenolith in ignimbrites. Xenolith
no. 1 is the type locality for thirteen minerals, including lakargiite,
chegemite, kumtyubeite,
bitikleite and
elbrusite.
Zirconium-bearing megawite occurs with
spurrite,
hydroxylellestadite,
rondorfite, wadalite,
minerals of the
reinhardbraunsite -
kumtyubeite series,
calcite and rarely periclase.
Accessory and rare minerals are represented by the
perovskite subgroup
minerals lakargiite and
perovskite, the
garnet supergroup
minerals kerimasite and
elbrusite, and by
srebrodolskite, and a mineral with the formula
Ca3TiFe2O8. Spurrite crystals are
embedded in the mass of secondary minerals among which
hydrocalumite,
ettringite group minerals,
hydrogrossular, afwillite
and other hydrosilicates are widespread. Brucite develops after
periclase.
Zirconium-bearing megawite crystals from the holotype sample do not
exceed 15 microns in size and usually occur as inclusions in spurrite.
Numerous lakargiite crystals occur between
spurrite grains in wadalite -
calcite - hydrocalumite -
ettringite aggregates. Homogeneous megawite and
lakargiite crystals are commonly found in the same
spurrite crystal
(MM 75.5.2563-2572).
The type locality for megawite is Xenolith no. 3, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky
District, Kabardino-Balkaria, Russia, which is also the type locality for
toturite, pavlovskyite and
rusinovite. Megawite was found here forming rims on micron-sized
lakargiite crystals in
larnite-cuspidine zones in
skarns which contain abundant
hydrogarnet and hydrosilicates. Megawite and
garnets (toturite and
tin-bearing schorlomite) form rims
on lakargiite pseudomorphs
after zircon. Megawite from xenolith no. 3 contains considerable
CaZrO3 and CaTiO3, and also U, Nb and Fe impurities
(MM 75.5.2563-2572).
Megawite from Xenolith no. 3 -
Image
At Xenolith no. 7, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District,
Kabardino-Balkaria, Russia, tin-rich
lakargiite was found, as well as the type specimens of
vorlanite and irinarassite.
Crystals of tin-rich lakargiite
overgrow porous, fine-grained aggregates of almost pure lakargiite, which
occur with relict larnite,
rondorfite, wadalite,
magnesioferrite,
arsenic-bearing
hydroxylellestadite and
srebrodolskite. Rarely, megawite occurs as rims up to 5 microns
thick on tin-rich lakargiite crystals
in the highly altered parts of the chegemite-bearing
skarns which contain
hydrogarnet and ettringite.
The megawite composition approaches the boundary with lakargiite. A
phase close to burtite, which overgrows the
lakargiite aggregates, is also found in this association.
Megawite crystals are transparent and pale yellow or colourless with a vitreous lustre and a white streak
(MM 75.5.2563-2572).
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