White and yellow crystal aggregates of the rare mineral Para-alumohydrocalcite from the type locality in Russia: Vodinskoe, Samara Oblast, Russian Federation. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Para-alumohydrocalcite
Para-alumohydrocalcite is an IMA-recognized mineral species in the carbonate class, with the chemical formula CaAl₂(CO₃)₂(OH)₄·6H₂O.
It is a member of the Alumohydrocalcite structural group.
Key properties: Mohs hardness 1.75; specific gravity 2; optically biaxial.
IMA symbol Pahcal, IMA status: approved, named in 1976.
Found in the oxidized zone of sulfur deposits, formed by decomposition of allophane (Vodin deposit, Russia; Gaurdak deposit, Turkmenistan).
It is found associated with Gypsum, calcite, halloysite (Vodin deposit, Russia; Gaurdak deposit, Turkmenistan); allophane, scarbroite, dundasite (Hampstead Farm quarry, England).
Its name comes from the Greek para, for near, and its relation to alumohydrocalcite.