Cyclosilicate (ring silicate), dimorph of catapleiite, benitoite group Specific gravity: 2.67
Colour: Colourless, may be pale yellow, pale brown to brown, pale grey, grey-green.
Solubility: Gelatises in acids Dana
Gaidonnayite occurs in altered pegmatites and miarolitic cavites in
nepheline syenite (Webmin).
At the type locality, the Poudrette quarry, Mont Saint-Hilaire, Montérégie, Québec, Canada, gaidonnayite occurs in altered pegmatite dikes in an intrusive alkaline gabbro-syenite complex, and rarely in miarolytic cavities in nepheline syenite and breccia cavities; also in an igneous sill in limestone (Dana, HOM). Associated minerals include siderite, analcime, hilairite, aegirine, calcite, albite, catapleiite, zircon, pyrochlore, ancylite and burbankite (HOM).
At the Kipawa syenite complex, Temiscamingue county, Quebec, Canada, gaidonnayite occurs in eudialyte-rich pegmatite lenses as a late-stage alteration product of vlasovite (Dana), associated with vlasovite, gittinsite and apophyllite (HOM).
At Narssarssuk, Greenland, Denmark, gaidonnayite occurs in a vein of aegirine syenite (Dana), associated with natrolite, aegirine, albite and siderite (HOM, Dana).
At Bronnebukta, Norway, gaidonnayite occurs in a nepheline syenite pegmatite (Dana).
Common impurities: Ti,Nb,Ca,K
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