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The dachiardite subgroup comprises:
dachiardite-Ca:
Ca2(Si20Al4)O48.13H2O
dachiardite-K:
K4(Si20Al4)O48.13H2O
dachiardite-Na:
Na4(Si20Al4)O48.13H2O
These minerals are tectosilicates (framework silicates), and members of the
zeolite group
Specific gravity: 2.14 to 2.21
Hardness: 4 to 4½
Streak: White
Colour: Colourless, white, pink, orange-red
Solubility: Decomposed by common acids
Environments:
Volcanic igneous environments
Pegmatites
Hydrothermal environments
Dachiardite is a hydrothermal zeolite that generally occurs in silica-rich
environments, in late stages of pegmatites and in Si-rich volcanic rocks, but also in
basalt and in hydrothermally altered tuffaceous
sediments. It may be associated with mordenite,
ferrierite and
heulandite, which, like dachiardite, are all
zeolites. At Yellowstone Park drill holes show temperatures of formation of
100 to 200oC
(Dana).
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