Formula: Ca6.4[H0.6Si2O7]2(OH)2
Sorosilicate (Si2O7 groups)
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° and 550° C at pressures ranging
between about 500 to 3500 bars
(MM 39.544-548).
At Carneal, Glenoe, County Antrim, Ulster, Northern Ireland, UK, killalaite is associated with
larnite, magnetite,
perovskite, spinel and
spurrite
(HOM).
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