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Formula: Ca4Si2O6(CO3)(OH)2
Unclassified silicate
Crystal System: Monoclinic
Specific gravity: 2.770 measured, 2.77 calculated
Hardness: 4
Streak: White
Colour: Light brown, white
Solubility: Decomposed by acids with effervesence
Common impurities: Al,Fe,Mg,Na,K,P
Environments
Fukalite is a retrograde mineral and alteration product in skarn
formed from metasomatism of limestone. Associated minerals include
cuspidine, xonotlite,
calcite, spurrite,
hillebrandite, scawtite,
foshagite, wollastonite,
fluorite, gehlenite,
perovskite, grossular,
hydrogrossular, vesuvianite
and monticellite
(HOM).
Localities
At the Eddy Creek quarry, Weld River district, Huon-Channel region, Huon Valley municipality, Tasmania, Australia,
fukalite has been found in a skarn deposit. Other minerals found in
the same deposit include artinite,
foshagite, hillebrandite,
mullite, plombièrite and
thaumasite
(AJM 18.1.65).
At Kushiro, Shoubara City, Hiroshima Prefecture, Japan, fukalite is an alteration product in
gehlenite-spurrite
skarn, associated with xonotlite,
calcite, spurrite,
scawtite, wollastonite,
gehlenite, grossular,
vesuvianite and monticellite
(https://rruff.info/rruff_1.0/uploads/MJ8_374.pdf).
At the Mihara mine, Higashi-Mihara, Ibara City, Okayama Prefecture, Japan, fukalite is an alteration product in
gehlenite-spurrite
skarn, associated with
cuspidine, xonotlite,
calcite, scawtite,
gehlenite, grossular,
hydrogrossular and vesuvianite
(https://rruff.info/rruff_1.0/uploads/MJ8_374.pdf).
At the type locality, the Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan,
skarn minerals such as spurrite,
gehlenite, perovskite and
rankinite were formed as products of
limestone. The skarn
contains retrograde minerals such as tilleyite,
kilchoanite and bicchulite, and
fukalite as one of the retrograde minerals of spurrite. The minerals
occur in the following zones, each zone being 2 cm or more in width and containing small amounts of
gehlenite, vesuvianite,
grossular and sometimes perovskite:
spurrite zone
fukalite-scawtite zone
fukalite zone
xonotlite-calcite zone
wollastonite-calcite-fluorite(-prehnite)
zone
fluorite-quartz zone
The fukalite zone has crystals of fukalite to 0.2 mm with minor
calcite and xonotlite and
cuspidine in scattered spots. Fukalite is also found in some
hillebrandite veinlets
(https://rruff.info/rruff_1.0/uploads/MJ8_374.pdf).
Alteration
Fukalite is decomposed by acids with effervesence. When heated it loses H2O and CO2 at
about 600oC with the formation of larnite. In hydrothermal
experiments at 1 kbar H2O pressure, fukalite was unchanged at 500oC and decomposed
irreversibly to calcite, foshagite
and dellaite above 550oC
(AM 63.793).
fukalite to larnite, CO2 and H2O
Ca4Si2O6(CO3)(OH)2 → 2Ca2(SiO4) +
CO2 + H2O
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