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Formula: Ca5(SiO4)2F2
Nesosilicate (insular SiO4 groups), chegemite subgroup,
humite group
Crystal System: Monoclinic
Specific gravity: 2.866 calculated
Hardness: 5 to 6
Streak: White
Colour: Light pink
Environments
Volcanic igneous environments
Metamorphic environments
Localities
At the type locality, Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District,
Kabardino-Balkaria, Russia, the central part of the xenolith is composed of bluish grey
marble with massive dark grey
spurrite - calcite rocks encasing
the marble core. Some small xenolith outcrops (1 to 1.5 m across) occur
along contacts of xenolith 1. They are light coloured from white to yellow or red and contain abundant calcium
minerals of the humite group, including
reinhardbraunsite and kumtyubeite. More rarely, small
fragments of light spurrite rocks, 50 cm in size, with striking pink spots
of reinhardbraunsite and yellow oval
rondorfite patches are noted. At the contact of the xenolith with
ignimbrites, cuspidine rocks
with larnite, rondorfite,
rustumite and wadalite are
developed. Reinhardbraunsite,
rondorfite, P- and As- bearing
hydroxylellestadite,
wadalite, Sn- and U- bearing
lakargiite, srebrodolskite
and magnesioferrite are commonly distributed in different types of
skarn rocks; perovskite,
kimzeyite-type garnet,
periclase and sphalerite are
considerably less abundant; secondary calcium hydrosilicates
(bultfonteinite,
hillebrandite and
afwillite), minerals of the
ettringite group,
hydrocalumite, hydrogarnets,
calcite and brucite are fairly
common.
Kumtyubeite is noted in spurrite -
rondorfite - ellestadite
zones of skarn. In hand specimens of the greyish-reddish matrix,
kumtyubeite forms oval spots up to 1 cm across, composed of light pink grains 250 µm in maximum dimension.
Rarely, kumtyubeite contains inclusions of lakargiite and
kimzeyite.
Rondorfite is also characteristically found in this association, occurring
as rounded, isometric inclusions in kumtyubeite, partly replaced by calcium hydrosilicates. P- and As-bearing
hydroxylellestadite associated with kumtyubeite is often
replaced by minerals of the ettringite group and hydrogarnets.
Accessory minerals are srebrodolskite and
magnesioferrite, forming aggregates reaching 500 µm in size, and also
kimzeyite-type garnet,
wadalite and sphalerite.
Reinhardbraunsite is confined to
spurrite zones of the skarn,
which change to kumtyubeite - spurrite -
rondorfite - ellestadite
zones toward the xenolith centre. Larnite relics are absent within
kumtyubeite and reinhardbraunsite
(AM 94.10.1361-1370).
Kumtyubeite from the Lakargi Mountain -
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