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Formula: Ca2(Si4Al4)O16.8H2O
Tectosilicate (framework silicate), zeolite group
Specific gravity: 2.12 to 2.28
Hardness: 4 to 5
Streak: White
Colour: Colourless, white, very pale pink
Environments:
Pegmatites
Sedimentary environments (tuff)
Metamorphic environments
Basaltic cavities
Gismondine-Ca is one of the rarer zeolites occurring in
silica-undersaturated environments,
intimately associated with phillipsite; it is likely that the
temperature of crystallizasion
is between 25°C and about 90°C (IZA). It occurs most commonly in
olivine
basalt, less commonly in
nepheline basalt, and
tuff, schist or
pegmatites.
In zeolite zones in basalt lavas it
is associated with chabazite,
thomsonite
and phillipsite
(DHZ 4 p407).
Localities
At Brisbane, Queensland, Australia, gismondine-Ca occurs in miarolitic cavities in
granite, associated with prehnite,
laumontite, and sulphides
(IZA).
At several localities in Austria gismondine-Ca occurs in cavities in nepheline
basalt associated with gonnardite and
phillipsite
(IZA).
At Ontario, Canada, gismondine-Ca occurs in metapyroxenite with other
zeolites
(IZA).
At Mont Saint Hilaire, Quebec, Canada, gismondine-Ca occurs in breccia cavities
in nepheline syenite, associated with
analcime
(IZA).
At Alexander dam, Hawaii, USA, gismondine-Ca has been reported in cavities associated with
stilbite, allophane,
olivine and augite
(DHZ 4 p407).
In Bohemia, Czech Republic, gismondine-Ca occurs in cavities in basalt and
leucite tephrite
(IZA).
In the Eifel District, Germany, gismondine-Ca occurs in vesicles in nepheline
basalt and in xenoliths in the basalt.
Associated minerals include phillipsite and
gonnardite
(IZA).
In eastern Iceland gismondine-Ca occurs in vesicles in olivine
basalt
(IZA).
At County Antrim, Northern Ireland, gismondine-Ca occurs in cavities in olivine
basalt flows
(IZA).
At the first recorded locality, Capo di Bova in the Rome area of Italy, gismondine-Ca occurs in cavities in
leucitic basalt at
(IZA).
At Round Top, Honolulu, Hawaii, USA, gismondine-Ca occurs in cavities in basalt and
in melilite nepheline in the
scoria cone
(IZA).
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