The erionites are:
Erionite-Ca, Ca5[Si26Al10O72].30H2O
Erionite-K, K10[Si26Al10O72].30H2O
Erionite-Na, Na10[Si26Al10O72].30H2O
They are all tectosilicates (framework silicates) and members of the zeolite group.
Specific gravity: 2.09 to 2.13
Hardness: 3½ to 4
Streak: White
Colour: Colourless, white, green, grey, orange

Volcanic igneous environments
Sedimentary environments
Basaltic cavities

Erionite is common in altered silicic tuff, especially in saline lake deposits, where it crystallises when the pH reaches about 8.5 (moderately alkaline). In this environment trivalent iron may substitute for aluminium in the structure (AM54.875-886).
Hydrothermal erionite occurs in cavities in volcanic rocks. It is often intergrown with offretite.
Epitaxial overgrowths of erionite on lévyne have been reported (AM83.577-589).

At Pauliberg, Burgenland, Austria, erionite needles are found on primary magnetite and hematite in vesicular basalt.

In the basalt at Kollnitz, Carinthia, erionite is found on celadonite associated with pyrite, calcite and phillipsite.

At Chase Creek, British Columbia, Canada, pure erionite without any offretite intergrowth occurs in vesicular basalt, rarely covered by paulingite, harmotome, heulandite and clay.

At Pass Valley, British Columbia, Canada, erionite intergrown with clay and associated with clinoptilolite occurs in vesicles in rhyolite.

At Twig Creek, British Columbia, Canada, erionite crystals capped by offretite line vesicles in basalt (ZoW161-162).

Erionite covered with chabazite occurs in basalt in the Faroe Islands, Denmark (ZoW161-162).

Near Araules, Auvergne-Rhône-Alpes, France, offretite intergrown with small amounts of erionite is found in basalt, associated with phillipsite, chabazite and calcite.

At Mont Semiol, Auvergne-Rhône-Alpes, France, erionite is found as terminations on offretite crystals in olivine basalt, associateed with mazzite, phillipsite, chabazite, calcite and siderite.


At Shurdo, Georgia, erionite occurs in volcanic rock associated with heulandite, chabazite, mordenite, stilbite and opal (ZoW161-162).

At Sasbach, Baden-Württemberg, Germany, offretite-erionite occurs in vesicles in nepheline - olivine - augite basalt, associated with faujasite and phillipsite.

At Teichelberg, Bavaria, Germany, offretite-erionite occurs in cavities in basalt associated with gismondine, phillipsite, calcite and chabazite.

At Wiesau, Bavaria, Germany, erionite-offretite occurs in basalt with thomsonite and montmorillonite.

At the Zeilberg Quarry, Bavaria, Germany, erionite is found in basalt with dachiardite, clinoptilolite, phillipsite, natrolite, heulandite, thomsonite, laumontite, scolecite, stilbite, gmelinite, chabazite, gismondine, apophyllite, calcite, gyrolite, okenite, garronite and tobermorite.

Near Gedern, Hessen, Germany, erionite is found in the extremities of offretite needles in vesicular basalt, associated with phillipsite, chabazite, montmorillonite and, rarely, gismondine.

At Geilhausen, Hessen, Germany, offretite covered by erionite occurs in vesicles in olivine basalt, associated with chabazite and phillipsite.

At Hungen, Hessen, Germany, erionite-offretite occurs with chabazite, faujasite, ferrierite, lévyne, phillipsite and thomsonite.

At the Ortenberg Quarry, Hessen, Germany, erionite is found, rarely, in vesicles in a sandstone xenolith embedded in olivine basalt, with paulingite, clinoptilolite, nontronite, phillipsite, calcite, dachiardite, merlinoite, apophyllite and chabazite (ZoW161-162).

At Nuoro, Sardinia, Italy, erionite is found as overgrowths on lévyne (ZoW161-162).

Erionite on lévyne crystals is found in vesicular basalts at Chojabaru, Nagasaki Prefecture, Japan, associated with chabazite and stilbite.

At Narushima, Nagasaki Prefecture, Japan, erionite occurs with heulandite in the glassy margins of a rhyolite dyke.

Along the seashore of Maze, Niigata Prefecture, Japan, erionite is found associated with chabazite (ZoW 161-162).

At Waitakere, North Island, New Zealand, erionite is found surrounded by lévyne.

At Moeraki, South Island, New Zealand, erionite occurs in altered vesicular basalt associated with chabazite, heulandite and phillipsite (ZoW161-162).

In lavas along the Nidym River, Siberia, Russia, erionite is associated with heulandite (ZoW161-162).

At Lake Natron, Arusha Region, Tanzania, erionite is associated with phillipsite, mordenite, analcime and chabazite.

In the Olduvai Gorge, Arusha Region, Tanzania, erionite is abundant in sedimentary beds associated with phillipsite, clinoptilolite, chabazite and analcime (ZoW161-162).

At Giant's Causeway, County Antrim, Northern Ireland, UK, erionite occurs in basalt associated with heulandite and phillipsite.

Erionite is often intergrown with offretite on lévyne at many localities in County Antrim, Northern Ireland, UK.

At the Storr, Isle of Skye, Scotland, UK, erionite occurs in vesicles in basalt with massive garronite (ZoW161-162).

Near Ajo, Arizona, USA, erionite occurs in vesicular basalt associated with phillipsite, heulandite and calcite on the primary minerals hematite, augite, kaolinite, enstatite, pseudobrookite and rancieite.

At Malpais Hill, Arizona, USA, in vesicular olivine basalt, small vugs are lined with celadonite and montmorillonite covered with offretite intergrown with erionite.

At Thum Butte, Arizona, USA, erionite occurs in vesicular olivine basalt associated with quartz, mordenite, clinoptilolite, phillipsite and opal.

Near Freedom, Idaho, USA, erionite occurs in vesicular basalt with chalcedony and opal.

At Reese River, Nevada, USA, erionite occurs in lacustrine (deposited in a lake) mudstone associated with clinoptilolite, chabazite and phillipsite.

Near Aneroid Lake, Oregon, USA, erionite occurs in vesicular basalt, frequently covered with heulandite.

At the Durkee fire-opal mine, Oregon, USA, some erionite fibres are found covered by common opal and, rarely, fire opal.

At Yaquina Head, Oregon, USA, erionite occurs in vesicular basalt associated with clinoptilolite, mordenite, phillipsite, pyrite and, rarely, dachiardite and baryte (ZoW161-162).

Along the Beaver Divide, Wyoming, USA, erionite and clinoptilolite occur in altered tuff.

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