Creedite

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Formula: Ca₃Al₂(SO₄)(OH)₂F₈.2H₂O
Compound halide
Crystal System: Monoclinic
Specific gravity: 2.713 to 2.73 measured, 2.715 calculated
Hardness: 4
Streak: White
Colour: White, violet, colourless; colourless in transmitted light
Solubility: Slowly soluble in acids
Environments

Hydrothermal environments

Creedite is an uncommon halide in fluorite-rich hydrothermal mineral deposits (HOM).

Localities

At the Akchatau Mine, Akchatau, Shet, Karaganda Region, Kazakhstan, creedite occurs with quartz (FM 81648).

At the Cresson open pit, Eclipse Gulch, Cripple Creek Mining District, Teller county, Colorado, USA, creedite has been found associated with celestine, gearksutite, pyrite and rhodochrosite. Gearksutite is generally the last of the minerals to form. Some specimens show celestine intergrown with or overlying creedite (Minrec 36.2.168).

At the the type locality, the Colorado Fluorspar Company Mine, Wagon Wheel Gap, Mineral county, Colorado, USA, creedite occurs in the upper portions of a fluorite - baryte vein, associated with fluorite, halloysite, baryte and kaolinite (AM 17.75-77, AM 37.787-790).
The host rock for the fluorite veins is Miocene-aged tuff, tuff breccia, and intermediate to silicic lava flows. Creedite was found in the widest portions of the veins where cavities in the massive fluorite existed. Other minerals found in these deposits were baryte, calcite, covellite, gearksutite, pyrite and quartz. The fluorite mineralisation probably originated with hot spring fluids, which precipitated fluorite and associated minerals at low confining pressures, ie at shallow depths (R&M 93.4.369-372).

At the small gold camp of Granite (now abandoned), Tonopah Mining District, San Antonio Mountains, Nye county, Nevada, USA, some specimens of the ore found in the small veins of the district in the oxidised zone contain creedite needles to 2mm, associated with fluorite and halloysite. The gold-bearing deposits here are apparently fluorite-quartz veins with free gold. The creedite probably results from the action of aluminium bearing solutions on fluorite. The gold of the veins is primarily inclosed in fluorite but some crystals of creedite were found with enclosed plates of gold, suggesting that the fluorite was removed and its place taken by creedite (AM 17.75-77, AM 37.787-790).

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