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Formula: Ca6.4[H0.6Si2O7]2(OH)2
Sorosilicate (Si2O7 groups)
Crystal System: Monoclinic
Specific gravity: 2.94 calculated
Streak: White
Colour: White, colourless in thin section
Environments
Metamorphic environments
Hydrothermal environments
Killalaite is a secondary mineral in cavities and veins
in hydrothermally
altered and thermally metamorphosed limestone
(Webmin, HOM).
Localities
At the type locality, Inishcrone, Killala Bay, Sligo County, Connacht, Ireland, the common
primary mineral assemblages in the order of increasing distance
from the
contact of limestone with
granite are:
gehlenite - larnite +/-
spurrite,
larnite -
spurrite +/- gehlenite,
spurrite - wollastonite -
rankinite - tilleyite +/-
cuspidine,
spurrite -
calcite +/- cuspidine,
calcite - wollastonite,
calcite - grossular
and
calcite - quartz.
The primary mineral assemblages have been altered by
hydrothermal activity.
Scawtite and cuspidine are the
main alteration
products of the spurrite-bearing rocks, and killalaite occurs either
with coarsely
crystallised calcite and afwillite
in veins and
cavities, or as replacements of tilleyite. Both
afwillite
and killalaite were formed later than scawtite,
cuspidine and tilleyite.
Killalaite and
afwillite formed before xonotlite.
Spurrite, wollastonite and
rankinite were formed at high temperature and very low pressure. The
stability field of
afwillite and killalaite lies between about 350°C and 550°C at
pressures ranging
between about 500 to 3500 bars
(MM 39.544-548).
At Xenolith no. 1, Lakargi Mountain, Upper Chegem volcanic caldera, Baksan Valley, Kabardino-Balkaria, Russia,
fluorchegemite was found in an
edgrewite-bearing zone of
endoskarn at the contact of a large altered calciferous xenolith within
ignimbrites.
Wadalite-eltyubyuite,
rondorfite, lakargiite and
kerimasite are high temperature accessory and minor minerals, whereas the
secondary minerals include
bultfonteinite, killalaite,
hillebrandite, afwillite,
trabzonite and jennite
(CM 53.325-344).
At Carneal, Glenoe, County Antrim, Ulster, Northern Ireland, UK, killalaite is associated with
larnite, magnetite,
perovskite, spinel and
spurrite
(HOM).
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