Formula: Ca2(Si4Al4)O16.8H2O tectosilicate
Specific gravity: 2.12 to 2.28
Hardness: 4 to 5
Colour: Colourless, white, very pale pink
Sedimentary environments (tuff)
Gismondine is one of the rarer zeolites; it occurs most commonly in
basalt, less commonly in
nepheline basalt, and
tuff, schist or
In zeolite zones in basalt lavas it is associated with chabazite, thomsonite and phillipsite (DHZ 4 p407).
At Alexander dam, Hawaii, USA, gismondine has been reported in cavities associated with stilbite, allophane, olivine and augite (DHZ 4 p407).
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