Gmelinite - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Hexagonal
    Chemistry : (Na2,Ca)Al2Si4O12 6H2O
    Rarity : Uncommon

Gmelinite is a sodium zeolite found in basalts and associated plutonic rocks, as well as in sodium pegmatites of alkaline rocks. Gmelinite is also known in basalt alteration products. It was named in honor of the German mineralogist and chemist Cristian Gottlob Gmelin, professor at the University of Tübingen (Germany). Gmelinite occurs in crystals of varied facies : pyramidal, tabular, rhombohedral, sometimes in hexagonal lamellae or short prisms, with frequently striated faces. Intergrowths with chabazite are not rare, forming buildings of 4 cm. Gmelinite is variously colored : from white to yellowish, greenish, orange to salmon, sometimes brown.

Main photo : Gmelinite from Cattignano quarry, San Giovanni Ilarione, Verona, Italy © Volker Betz

Gmelinite from Road Cut SW, Avhellero, Larnaca, Cyprus © Volker Betz
Sceptred gmelinite from Magheramorne, Northern Ireland © Volker Betz
2 cm gmelinite from Two Islands, Nova Scotia, Canada © Volker Betz
Gmelinite from Pinnacle Rock, Five Islands, Nova Scotia, Canada © Donald Doell

Gmelinite in the World

Although gmelinite deposits are quite numerous, it is never present in significant quantities. The most beautiful crystals, 4 cm specimens, were discovered in Tomohevitra (Madagascar) and Frankston near Melbourne (Australia). Splendid centimeter-sized pink crystals were extracted from basalt quarries in New Jersey, particularly in Paterson. Rare gmelinite crystals are occasionally found in classic zeolite deposits: Bay of Fundy (Nova Scotia, Canada), Northern Ireland, Vesuvius and Cabo di Bove (Italy), or Springfield (Oregon). In the more original context of alkaline massifs, gmelinite is reported at Mont-St-Hilaire (Quebec), at Ilimaussaq (Narssaq, Greenland), and at Lovozero (Kola, Russia).

Gmelinite in France

In France, gmelinite is reported in French Polynesia in the Tuamotu archipelago in Fangataufa.

Twinning

Twins are known on {10-11}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 4.5
Density : 2.11
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.477 to 1.485
Birefringence : 0.008
Optical character : Uniaxial +/-
Pleochroism : Low
Fluorescence : blue to white

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None

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