Gmelinite-Na
Gmelinite-Na is one of the rarest of the Zeolite Group of minerals that includes over 40 minerals and these minerals that are gem-type Analcime, Barrerite, Chabazite, Epistilbite, Gmelinite-Na, Goosecreekite, Mordenite, Natrolite, Pollucite, Scolecite, Stellerite, Stilbite, Thomsonite and Yugawaralite. Most of these minerals are typically found only as extremely fine, radiating needles, cottony aggregates or radiating masses so gem quality crystals are notably rare. Gmelinite crystals however, are hexagonal in outline and dipyramid (two pyramids which can be identical the very best and bottom).
Widespread in lower amounts. A localities that are few well studied product follow. From Montecchio Maggiore, Vicenza, Italy. At Glenarm and elsewhere in County, Antrim, Ireland. Regarding the Isle of Skye, Scotland. At Pyrgos, Cyprus. On Pinnacle Rock, Five Isles, and Two Islands, Nova Scotia, Canada. In the Il¶³maussaq intrusion, southern Greenland. At Sarbay-Sokolov, Kazakhstan. Large crystals from Bekiady, Madagascar. From around Flinders, Victoria, Australia. In the USA, from Bergen Hill, Hudson County, and Great Notch, Paterson, and Prospect Park, Passaic County, New Jersey; at Springfield, Lane County, Oregon.
| Crystallography: | Hexagonal – Dihexagonal Dipyramidal |
| Crystal Habit: | As euhedral crystals, pyramidal, tabular, or rhombohedral, striated || (0001) or less commonly, || [0001], to 4 cm. Rarely in radiating aggregates or granular. |
| Twinning: | Penetration twins on {1011}, common. |
| Cleavage: | [1010] Distinct |
| Fracture: | Vitreous |
| Tenacity: | Brittle |
| Hardness (Mohs): | 4.5 |
| Density: | 2.02 – 2.17 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 4.58 (Gamma Ray American Petroleum Institute Units) |
| Other: | Piezoelictric |
| Color: | Colorless, White, Reddish White, Salmon-Red, Yellowish, Greenish White; Colorless in thin section |
| Transparency: | Transparent to Translucent, Opaque |
| Luster: | Vitreous |
| Refractive Index: | 1.474 – 1.494 Uniaxial ( +/- ); may be anomalously Biaxial |
| Birefringence: | 0.0020 – 0.0130 |
| Dispersion: | Strong |
| Pleochroism: | None |
