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Formula: Ca2(Si4Al4)O16.8H2O
Tectosilicate (framework silicate), gismondine subgroup,
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 crystallisation
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).
Gismondine-Ca from Austria - Image
At Ontario, Canada, gismondine-Ca occurs in metapyroxenite
with other
zeolites
(IZA).
At the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada,
gismondine-Ca occurs in breccia cavities
in nepheline syenite, associated with
analcime
(IZA).
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).
In Liguria, Italy, (possibly Rio Pian del Foco, Olbicella, Molare, Alessandria Province, Piedmont, Italy)
gismondine-Ca occurs in veins and intensely sheared rocks of the
pumpellyite-actinolite facies, and in
serpentinite
(IZA).
At the first recorded locality, Capo di Bove, Rome, Metropolitan City of Rome Capital, Lazio, Italy, gismondine-Ca
occurs in cavities in
leucitic basalt
(IZA).
Gismondine-Ca from Capo di Bove - Image
At the Bruslee quarry, Ballyclare, Co. Antrim, Northern Ireland, UK, gismondine-Ca occurs in cavities in
olivine
basalt flows
(IZA).
At Round Top, Honolulu, Oahu Island, Honolulu County, Hawaii, USA, gismondine-Ca occurs in cavities in
basalt and
in melilite nepheline in the
scoria cone
(IZA).
Gismondine-Ca from Oahu Island - Image
At Alexander Dam, Kauai Island, Kauai County, Hawaii, USA, gismondine-Ca has been reported in cavities associated
with stilbite, allophane,
olivine and augite
(DHZ 4 p407).
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