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Formula: Ca9(SiO4)4F2
Nesosilicate (insular SiO4 groups), chegemite subgroup,
humite group, forms a series with
hydroxyledgrewite
Crystal System: Monoclinic
Specific gravity: 2.919 calculated
Hardness: 5½ to 6½
Streak: White
Colour: Colourless, white in aggregates
Environments
Localities
At the type locality, Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Baksan Valley,
Kabardino-Balkaria, Russia, members of the edgrewite -
hydroxyledgrewite series were discovered in xenoliths of
carbonate-silicate rock altered to skarn within
ignimbrites. The new minerals occur sparingly in zones
containing bultfonteinite,
hillebrandite, jennite and
chegemite, as well as rare relics of
larnite and rondorfite enclosed
in a matrix of hydroxylellestadite. Edgrewite and
hydroxyledgrewite are largely altered to
jennite in places with admixed
zeophyllite and trabzonite,
and are preserved as elongate relics mostly 0.1–0.4 mm long in the central part of atoll-like
pseudomorphs
(AM 97.1998-2006).
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