Fukalite

fukalite

gehlenite

spurrite

hillebrandite

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Formula: Ca4Si2O6(CO3)(OH)2
Unclassified silicate
Specific gravity: 2.770
Hardness: 4
Streak: White
Colour: Light brown, white
Solubility: Decomposed by acids with effervesence
Common impurities: Al,Fe,Mg,Na,K,P
Environments

Metamorphic 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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