Gmelinite-Na is one of the rarer zeolites but the most common member of the gmelinite series, gmelinite-Ca, gmelinite-K and Gmelinite-Na. It is closely related to the very similar mineral chabazite. It is generally assumed that it forms at low temperatures, less than 100°C.
Gmelinite was named as a single species in 1825 after Christian Gottlob Gmelin (1792–1860) professor of chemistry and mineralogist from Tübingen, Germany, and in 1997 it was raised to the status of a series.
- Category: Zeolites
- Formula: Na4(Si8Al4)O2411H2O
- Crystal system: Hexagonal
- Crystal class: Dihexagonal dipyramidal (6mmm)
The naturally occurring mineral forms striking crystals, shallow, six-sided double pyramids, which can be colorless, white, pale yellow, greenish, orange, pink, and red. They have been compared to an angular flying saucer.
- Formula mass: 2,000.77 g
- Color: Colorless, white, yellow, orange, pale green, pink, red, brown and grey
- Crystal habit: Hexagonal plates, or short prisms, showing hexagonal dipyramids, pyramids, and basal pinacoid.
- Fracture: Conchoidal
- Tenacity: Brittle
- Mohs scale hardness: 4 1⁄2
- Luster: Dull to vitreous
- Streak: White
- Diaphaneity: Transparent, translucent or opaque
- Specific gravity: 2.04 to 2.17
- Optical properties: Uniaxial (-)
Gmelinite-Na occurs extremely rarely at the Francon Quarry, Montreal, Canada, in sills of the igneous volcanic rock phonolite which are rich in dawsonite, NaAl(CO3)(OH)2. It occurs both as pure Gmelinite-Na and interlayered with chabazite in water-quenched basalts in Western Tasmania. It also occurs in Na-rich pegmatites in alkaline rocks, and as an alteration product in some nepheline syenite intrusions. No sedimentary gmelinite has been found.
Associated minerals include other zeolites, especially chabazite, quartz, aragonite, and calcite.
Type Locality: Monte Nero, San Pietro, Montecchio Maggiore, Vicenza Province, Veneto, Italy. Also found in Australia, Canada, Czech Republic, Germany, Hungary, Japan, Russia, UK, and US.