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Formula: (Na,Ca)2(Si,Al)5O10.3H2O tectosilicate (framework silicate),
zeolite group
Crystal System: Orthorhombic
Specific gravity: 2.25 to 2.36 measured, 2.33 calculated
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, yellow, pink to salmon-orange
Environments:
Volcanic Igneous environments
Pegmatites
Metamorphic environments (rarely)
Basaltic cavities
Gonnardite occurs as a secondary mineral in silica-poor
volcanic rocks and pegmatites, and rarely in
skarn. Crystals are often found with cores of gonnardite and rims
of thomsonite. It also forms overgrowths on
natrolite.
Localities
At Abbotsford and Bundoora, inner Melbourne, Victoria, Australia,
gonnardite-natrolite occurs
in cavities in basalt
associated with chabazite and calcite or with
phillipsite and thomsonite
(AJM 20.1.44-46).
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