DACHIARDITE

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Monoclinic
    Chemistry : Na4Al4Si20O48 13H2O
    Rarity : Very rare

Dachiardite is a very rare zeolite, which forms a continuous series with its sodium equivalent, sodium-dachiardite. It is found in basalt cavities, hydrothermal veins and pegmatites, as well as in hydrothermalized volcanic tuffs. It is a colorless to yellowish zeolite which associates with heulandite, mordenite and ferrierite. It was named in honor of mineralogy professor Antonio D'Achiardi of the University of Pisa who described the mineral. The crystals are lamellar or fibrous prisms not exceeding 5 mm, sometimes grouped in radiated aggregates.

Main photo : Dachiardite from Altoona, Washington, USA © Rudy Tschernich

Dachiardite from Opal Hill Mine, California, USA © Volker Betz
Cyclically twinned dachiardite from San Piero in Campo, Elba Island © Gianfranco Ciccolini
Dachiardite from Tanzenberg, Styria, Austria © Volker Betz
Dachiardite from Csák Hill, Márianosztra, Hungary © Volker Betz

Dachiardite in the World

Very beautiful samples come from the pegmatites of San Piero in Campo (Island of Elba, Italy) where 5 mm twinned crystals accompany the rubellite. Dachiardite is also known in classic zeolite sites, such as the basalt cavities of Oregon (Agate Beach, Cape Lookout, etc...), the Lower Geyser Basin (Yellowstone Park, Wyoming), or the basalts of Japan. It is also found in the alpine clefts of Alpe di Siusi (Trentino, Italy).

Dachiardite in France

In France, dachiardite is only reported from the Kerguelen Islands.

Twinning

A twin on {110} is known and can be cyclical eightlings.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 4 to 4.5
Density : 2.16
Fracture : Conchoidal
Streak : White

TP : Transparent
RI : 1.488 to 1.499
Birefringence : 0.006
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Acids


Magnetism : None
Radioactivity : None