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Formula: Ca9(Ca0.5◻0.5)Mg(PO4)7
Phosphate, merrillite subgroup,
merrillite group,
cerite supergroup
Crystal System: Trigonal
Specific gravity: 3.122 calculated
Streak: White
Colour: Colourless
Luminescence: Not fluorescent under UV
Environments
Metamorphic environments
Meteorites
Keplerite is a new mineral, approved in 2020, that occurs in some pallasite and angrite
meteorites. It is an indicator of high-temperature
environments characterised by extreme depletion of Na
(HOM).
Localities
At the Aravaite type locality, Hatrurim Basin, Tamar Regional Council, Southern District, Israel, keplerite
occurs in brecciated, altered
pyroxene paralava (fused
sediments) by pyrometamorphism. Associated minerals include fluorapatite,
maghemite and stanfieldite
(HOM).
The association of keplerite with “REE -
merrillite” and stanfieldite
provides evidence for the similarity of temperature conditions that occurred in the Mottled Zone (Hatrurim Formation)
to those expected during the formation of pallasite meteorites
and lunar rocks
(AM 106.1917-1927)
At the type locality, the Marjalahti meteorite, Viipuri, Ladoga Region, Republic of Karelia, Russia, keplerite
occurs in the main-group pallasites and angrites. It is the
Ca-dominant counterpart of the most abundant meteoritic phosphate, which is
merrillite. The Marjalahti meteorite is the main group
pallasite.
Keplerite grains in Marjalahti have an ovoidal to cloudy shape and reach 50 μm in size. The mineral is
colourless and transparent with a vitreous lustre. Cleavage was not observed. In transmitted light, keplerite is
colourless and non-pleochroic. It is an indicator of high temperature environments characterised by extreme depletion
of Na. The association of keplerite with “REE -
merrillite” and stanfieldite
provides evidence for the similarity of temperature conditions that occurred in the Mottled Zone (Hatrurim Formation)
to those expected during the formation of pallasite meteorites
and lunar rocks
(AM 106.1917-1927)
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