Metavariscite

metavariscite

fluellite

variscite

montgomeryite

Images

Formula: Al(PO4).2H2O
Hydrated phosphate, metavariscite group, the monoclinic paramorph of orthorhombic variscite
Crystal System: Monoclinic
Specific gravity: 2.51 to 2.54 measured, 2.53 calculated
Hardness: 3½
Streak: White
Colour: Light green; colourless in transmitted light

Environments:

Hydrothermal environments

Metavariscite occurs commonly as a product of weathering phosphatic rocks; it may form as concretions by the phosphatisation of kaolin during weathering, and it is probably a reaction product of phosphate fertiliser in acid soil (HOM). Common associates include fluellite, montgomeryite and variscite (Mindat).

Localities

At the Milgun Variscite Mine, Milgun Station, Meekatharra Shire, Western Australia, veins of "variscite" are commonly a mixture of variscite and metavariscite. The veins may be altered and replaced by secondary minerals including montgomeryite, hydroxylapatite, strengite and leucophosphite. Variscite/metavariscite also forms pseudomorphs after pyrite (AJM 20.2.31-32).

At the Woodlands variscite gold occurrence, Woodlands Station, Meekatharra Shire, Western Australia, variscite/metavariscite occurs intergrown with extremely fine-grained quartz (AJM 14.1.28-30).

At Malpelo Island, San Andrés y Providencia Department, Colombia, metavariscite occurs in phosphatised andesite (Dana).

At the Gunheath China Clay Pit, Stenalees, Treverbyn, Cornwall, England, UK, variscite is uncommon, typically occurring as spherulitic aggregates of virtually colourless crystals, many of which contain white powdery cores up to 1 millimetre in diameter. The cores are composed of variscite along with variable amounts of metavariscite. The composition of the cores is similar to that of the surrounding variscite spherule, but additionally containing traces of K, Si and Fe.
Variscite and metavariscite typically occur on a matrix of granite pegmatite or coarse quartz-tourmaline vein material. Cassiterite occurs in the matrix of several specimens, wavellite is a common and intimate associate, and turquoise occurs on variscite on one specimen. Many crystals of metavariscite are enclosed by partial or complete brown transparent vitreous crusts to 0.1 mm thick of pure variscite, although the brown colour is unusual. Wavellite occurs on one specimen as sprays of acicular crystals to 3 mm intimate with, and often penetrating, variscite (MM 60.4.671-672).

At the Candelaria Mining District, Esmeralda county, Nevada, USA, massive metavariscite occurs with variscite (Dana).

At the Argentum Mining Co. Mine, Candelaria Mining District, Mineral County, Nevada, USA, whiteite-(CaMgMg) is a low temperature, secondary mineral presumed to have formed as a result of hydrothermal alteration. It is associated with crandallite, fluorwavellite, montgomeryite and variscite/metavariscite (CM 54.1513-1523).

At the type locality, the Edison Bird mine, Utahlite Hill, Lucin Mining District, Box Elder county, Utah, USA, metavariscite occurs as sedimentary phosphate mineralisation along fractures, associated with variscite (Mindat).

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