When perfused with boric and fluoric vapors from the granite they may contain much axinite, fluorite and datolite, but the altiminous silicates are absent from these rocks.
2.
It occurs as a primary mineral in nepheline syenites, within hydrothermal cavities in basalts and diabase and in serpentinites in association with zeolites, datolite, prehnite, calcite and serpentine.
3.
Though not a zeolite, prehnite is found associated with minerals such as datolite, calcite, apophyllite, stilbite, laumontite, heulandite etc . in veins and cavities of basaltic rocks, sometimes in granites, syenites, or gneisses.
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