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Formula: Ca2(Si20Al4)O48.13H2O
Tectosilicate (framework silicate), dachiardite subgroup,
zeolite group
Crystal system: Monoclinic
Specific gravity: 2.165 to 2.206 measured, 2.1395 calculated
Hardness: 4 to 4½
Streak: White
Colour: Colourless
Environments
Volcanic igneous environments
Pegmatites
Hydrothermal environments
Dachiardite-Ca is of hydrothermal origin in basalt,
quartz veins and
pegmatites; also in
tuffaceous sediments. Associated minerals include
mordenite, heulandite
and ferrierite
(HOM).
Localities
The type locality is La Speranza, San Piero in Campo, Campo nell'Elba, Livorno Province, Tuscany, Italy.
Dachiardite-Ca from La Speranza -
Image
At Yellowstone National Park, Wyoming, USA, dachiardite (renamed dachiardite-Ca in 1997) crystals have been
identified in a few isolated fractures and cavities within hydrothermally altered
rhyolite flows, tuffs,
and glacial sediments in drill-core samples. The dachiardite crystals are chemically inhomogeneous and
contain higher concentrations of calcium than previously reported from other areas. A nearly continuous
solid-solution series between dachiardite-Ca and
dachiardite-Na may exist, although data suggest a gap for
intermediate compositions due to greater potassium concentrations. The Yellowstone dachiardite precipitated
from thermal waters, at approximately 100 to 200oc, along with several other calcium-rich
zeolites, including
yugawaralite, mordenite and
epistilbite, as well as other calcium-bearing minerals
(CM 25.3.475-483),/i>.
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