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Formula: Ca9(SiO4)4(OH)2
Nesosilicate (insular SiO4 groups),
chegemite subgroup,
humite group
Crystal System: Monoclinic
Specific gravity: 2.918 calculated
Hardness: 5½ to 6
Streak: White
Colour: Colourless, white in aggregates
Environments
Hydroxyledgrewite is a relatively new mineral, approved in 2011 and to date (August 2026) reported only
from the type locality.
Localities
At the type locality, Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District,
Kabardino-Balkaria, Russia, members of the hydroxyledgrewite -
edgrewite series were discovered in xenoliths
of carbonate-silicate rock altered to
sanidinite facies
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.
Hydroxyledgrewite and edgrewite are largely altered to
jennite in places with admixed
zeophyllite and
trabzonite, and are preserved as elongate relics mostly 0.1 to
0.4 mm long in the central part of atoll-like pseudomorphs
(AM 97.11.1998-2006, HOM).
Hydroxyledgrewite from Xenolith no. 1,
Lakargi Mountain - Image
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