Formula: Ca2(PO3OH)(SO4).4H2O
Compound phosphate
Specific gravity: 2.30 to 2.34
Hardness: 1 to 1½
Streak: Pale yellow
Colour: Light yellow, yellow, brownish yellow, colourless

Cave deposits

Ardealite occurs in limestone caves, as a secondary mineral formed at an early stage of the breakdown of bat guano, in reaction with calcite. Associated minerals include brushite, gypsum, carbonate-rich hydroxylapatite, newberyite and taranakite (HOM).


At the type locality, the Cioclovina cave, Boșorod, Hunedoara, Hunedoara, Romania, ardealite is found in phosphate earth deposits associated with gypsum and brushite (AM 17.251). The ardealite derives from the reaction between calcium carbonate from the moonmilk flows or the cave floor and phosphoric solutions derived from bat guano, with or without hydroxylapatite as a precursor, at pH values up to 5.5 (EJM 29.1055-1066).

The Măgurici Cave, Sălaj, Romania, hosts a diverse assemblage of minerals. The phosphatisation of illite and montmorillonite clay-rich sediments, located on the cave's floor, lead to the formation of taranakite and francoanellite. Mineral assemblages precipitated at the boundary between limestone bedrock and guano deposits are dominantly hydroxylapatite, brushite, ardealite and monetite. A number of sulphate minerals, such as gypsum, bassanite, mirabilite and cesanite, were precipitated along with the phosphates (EJM 15.741-745).

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