Gmelinite is the name for three minerals:
Gmelinite-Ca: Ca2(Si8Al4)O24.11H2O
Gmelinite-K: K4(Si8Al4)O24.11H2O
These minerals are tectosilicates (framework silicates), zeolite group
Specific gravity: 2.04 to 2.17
Hardness: 4½
Streak: White
Colour: Colourless, white, yellow, greenish white, orange, pale green, pink, red, brown and grey

Metamorphic environments
Hot spring deposits
Hydrothermal environments
Basaltic cavities

Gmelinite generally occurs in cavities in silica-poor volcanic rocks, and also in sodium-rich pegmatites and 55 to 75oC geothermal wells. No sedimentary gmelinite has been reported. It is a product of diagenetic reactions, hydrothermal activity or alteration of basalt. Common associates are other zeolites, quartz, aragonite and calcite (Dana).

In the zeolite localities of Northern Ireland gmelinite is associated with chabazite, thomsonite, analcime, phillipsite, lévyne, calcite and aragonite (DHZ 4 p400).

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