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Formula: Ca12Fe3+10Si4O32Cl6
Nesosilicate (insular SiO4 groups), wadalite group
Crystal System: Isometric
Specific gravity: 3.349 calculated
Colour: Yellow to light brown, brown
Environments
Volcanic igneous environments
Metamorphic environments
Localities
At the Shadil-Khokh volcano, Kel’ volcanic area, Greater Caucasus Mountain Range, South Ossetia, Georgia, xenoliths
up to 3 m across have been found with rondorfite in
andesite-dacite lava.
Tetrahedral eltyubyuite crystals were found in a thin vein (3 mm) enriched with
magnetite,
magnesioferrite,
srebrodolskite, harmunite
and cuspidine cutting
larnite-rondorfite rock with
subordinate wadalite and
fluorellestadite
(EJM 25.2.221-229).
At the Bellerberg volcano, Vordereifel, Mayen-Koblenz, Rhineland-Palatinate, Germany, eltyubyuite was found
in xenoliths enriched with rondorfite and
fluorellestadite from volcanic rocks. In addition to minerals of
the mayenite supergroup,
kerimasite, magnetite,
magnesioferrite,
srebrodolskite and
manganese-bearing harmunite were
identified
(EJM 25.2.221-229).
At the type locality, Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Chegemsky District,
Kabardino-Balkaria, Russia, eltyubyuite was discovered in an altered calc-silicate xenolith
in ignimbrite. In this area large (2 to 3 m) carbonate xenoliths were
metamorphosed under sanidinite facies conditions.
Eltyubyuite is found as micrometre-sized inclusions in rondorfite.
Numerous inclusions of eltyubyuite, srebrodolskite and
perovskite up to 4 mm in size and of
larnite are concentrated in the external zones of
rondorfite crystals. Zoned crystals with
wadalite core and eltyubyuite rim are commonly present. Much rarer
are relatively large eltyubyuite crystals about 10 microns in size occurring on the border of
larnite and rondorfite crystals
in altered larnite zones, where
edgrewite -
hydroxyledgrewite and
fluorchegemite are noted.
High-temperature minerals in rocks containing eltyubyuite are
larnite, rondorfite,
wadalite,
hydroxylellestadite,
edgrewite -
hydroxyledgrewite,
chegemite-fluorchegemite
and cuspidine. Lakargiite,
perovskite, kerimasite,
srebrodolskite and
dovyrenite are accessory minerals.
Wadalite is widely distributed in the altered
larnite skarn zone; its
concentration in larnite grains near their contacts with
rondorfite crystals is noteworthy, whereas eltyubyuite,
srebrodolskite and
perovskite inclusions are enclosed in
rondorfite.
Bultfonteinite,
hillebrandite, jennite,
afwillite, zeophyllite,
reinhardbraunsite,
killalaite, trabzonite,
grossular–katoite,
hydrocalumite and minerals of the
ettringite series are widespread,
secondary low-temperature minerals.
The formation of the Fe3+ minerals eltyubyuite and
srebrodolskite is attributed to oxidation of Fe2+ in
rondorfite, an early formed mineral that in the
eltyubyuite-bearing samples has a relatively high Fe content, up to 3 wt. % FeO substituting for Mg
(EJM 25.2.221-229).
Eltyubyuite from the Lakargi Mountain -
Image
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