Alumohydrocalcite - Encyclopedia

    Class : Carbonates, Nitrates, Borates
    Subclass : Hydrous carbonates
    Crystal System : Triclinic
    Chemistry : CaAl2(CO3)2(OH)4 3H2O
    Rarity : Uncommon

Alumohydrocalcite is a hydrated carbonate of calcium and aluminum which forms chalky masses composed of fibrous crystals, white to pale blue, sometimes more intense blue, or greyish-green to olive-green, it is also frequently encountered in small millimetric spherolites. It owes its name to its chemical composition. It is a carbonated medium mineral whose formation seems to adapt to various conditions : alteration of allophane or dolomite, xenoliths of basic lava, etc...

The photo shows alumohydrocalcite pompoms from the Graulay basalt quarry (Germany) - Photo © Matteo Chinellato.

Aluminohydrocalcite from Les Mas Dieu, Gard, France - © Jean-Marc Johannet
Aluminohydrocalcite from Valcroze, Gard, France - 
© François Le Gaillard
Aluminohydrocalcite from Piast Mine, Pologne - © Eugene & Sharon Cisneros
Aluminohydrocalcite from Les Mas Dieu, Gard, France - © Joachim Esche

Alumohydrocalcite in the World

Alumohydrocalcite is a recognized mineral in many sites around the world. It is found in allophane alteration at Khakhassia (Russia), in the xenoliths of the Graulay basalt quarry (Germany). It is also known in Visé (Belgium), Mount Hamilton (California) and in many other localities.

Alumohydrocalcite in France

In France, alumohydrocalcite is known in very pretty little white pompoms at Mas Dieu and Valcroze (Gard).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake reported for this mineral species, but can easily be confused with other species of the same habitus.


Hardness : 2,5
Density : 2.2
Fracture : Irregular
Trace : White


TP : Opaque to transparent
RI : 1.485 to 1.585
Birefringence : 0,085
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric and nitric acid

Magnetism : None
Radioactivity : None