Gonnardite

tectosilicate

thomsonite

Formula: (Na,Ca)2(Si,Al)5O10.3H2O tectosilicate (framework silicate), zeolite group
Specific gravity: 2.21 to 2.36
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 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.

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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