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Formula: MgSiO3
Oxide, ilmenite group, high-pressure
paramorph of bridgmanite,
clinoenstatite and
enstatite
Crystal System: Trigonal
Specific gravity: 4.0 calculated
Streak: White
Colour: Colourless
Environments
Localities
The type locality is the Tenham meteorite, Tenham Station, Windorah, Barcoo Shire, Queensland, Australia. This
meteorite consists mainly of olivine,
enstatite, diopside,
plagioclase that has been partly converted to
maskelynite, an
iron-nickel alloy and
troilite. It was very strongly shocked, and a network of shock-induced
melt veins ≤ 1 mm in width runs across the entire body. Host minerals are enclosed as multiphase fragments in
shock veins and are partially or totally transformed into high-pressure phases.
Olivine in the walls of the veins is also partially converted to blue
ringwoodite. The black matrix of the vein is dominated by aluminous
majorite and lesser
magnesiowüstite, native iron,
iron-oxide, and iron-sulphide.
Electron microscope examination of three shock veins revealed that in one vein akimotoite existed as
aggregates adjacent to clinoenstatite (converted from
enstatite by the shock event) in fragments
(AM 84.267-271).
At the Sixiangkou meteorite, Sixiangkou, Gaogang District, Taizhou, Jiangsu, China, evidence has been found for high
ferric iron to total iron (Fe3+/ΣFe) ratios in aluminium-bearing
akimotoite co-existing with other high-pressure silicates and
iron-nickel metal from shock
melt-veins in the chondrite meteorite. The results
demonstrate that akimotoite in shock-melt veins of this meteorite has high proportions of Fe3+,
with a Fe3+/ΣFe ratio of 0.67(3). In contrast, the coexisting
majoritic garnet and
ringwoodite, which are the typical
iron-bearing phases in shock veins in this meteorite, are enriched in
Fe2+ rather than Fe3+, with Fe3+/ΣFe ratios of 0.10(5) and 0.15(5), respectively
(AM 92.1545-1549).
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