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Formula: Ca2(SO4)(CO3).4H2O
Compound sulphate
Crystal System: Orthorhombic
Specific gravity: 2.21 measured, 2.239 calculated
Hardness: 2
Streak: White
Colour: White, colourless
Environments
Localities
At the type locality, Rapid Creek, Dawson mining district, Yukon, Canada, rapidcreekite forms radiating acicular
crystals up to 2 mm long. It occurs as a secondary phase on
dilated joint-surfaces and bedding planes in a blocky, quartz-rich bed in the
sideritic iron formation. Minor amounts
of gypsum and aragonite are associated
with rapidcreekite, and kulanite is found on the holotype specimen
(CM 24.51-54).
The Diana Cave, Cerna valley, Caraş-Severin, Romania, develops along a fault line and hosts a spring of hot (51°C),
sulphate-rich, sodium-calcium-chloride bearing water of near-neutral pH. Abundant steam and H2S rises from the
thermal water to condensate on the walls and ceiling of the cave. The sulphuric acid produced by H2S oxidation
and hydrolysis causes a strong acid-sulphate weathering of the cave bedrock generating a sulphate-dominated mineral
assemblage that includes rapidcreekite closely associated with gypsum and
halotrichite group minerals. Rapidcreekite forms bundles of
colourless tabular orthorhombic crystals up to 1.5 mm in length
(AM 98.1302-1309).
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