By Andrew Silver, USGS.Materialscientist at en.wikipedia [Public domain or Public domain], from Wikimedia Commons
A variety called elaeolite is red, green, brown, or gray, massive or in crystals filled with minute inclusions. These inclusions produce a sheen that yields a catseye effect in cabochons. Facetable nepheline is a great rarity, and very few gems have been cut, always in the 1-2 carat range or smaller.
| Data | Value |
|---|---|
| Name | Nepheline |
| Varieties | Elaeolite |
| Scientific Name | Nepheline |
| Crystallography | Hexagonal. Crystals stumpy, sometimes very large; massive, compact; in grains. |
| Crystallographic Forms | |
| Refractive Index | 1.526-1.546 |
| Colors | Colorless, white, gray, yellowish, greenish, bluish, dark green, brick red, brownish red. |
| Luster | Vitreous to greasy. |
| Hardness | 5.5-6 |
| Fracture | Subconchoidal |
| Specific Gravity | 2.55-2.66 |
| Birefringence | 0.004 |
| Cleavage | Indistinct |
| Dispersion | Low. |
| Stone Sizes | Cabochons of nepheline have been cut in various sizes; crystals, especially those from Canada, can reach enormous size but are not attractive. Faceting material is extremely rare and very small. |
| Luminescence | Medium light blue (Germany) or medium dull orange (Ontario) in LW. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long |
| Transparency | Transparent to opaque. |
| Absorption Spectrum | Not diagnostic. |
| Phenomena | Chatoyancy. |
| Formula | (Na,K)AlSiO4. |
| Optics | o = 1.529-1.546; e = 1.526-1.542. Uniaxial (-). |
| Optic Sign | Uniaxial - |
Optics: o = 1.529-1.546; e= 1.526-1.542.
Uniaxial (-).
Occurrence: Plutonic and volcanic rocks; pegmatites associated with nepheline syenites.
Julienhaab district, Greenland; Langesundsfford, Norway;
China; Germany; Finland; Russia; Myanmar; North Korea; South Korea.
Various localities in the United States, especially Maine and Arkansas.
Ontario, Canada: crystals up to 15 inches long (non-gemmy).
Vesuvius, Italy: small, glassy transparent grains.
Comments: A variety called elaeolite is red, green, brown, or gray, massive or in crystals filled with minute inclusions. These inclusions produce a sheen that yields a catseye effect in cabochons. Facetable nepheline is a great rarity, and very few gems have been cut, always in the 1-2 carat range or smaller.
Name: From a Latin word meaning cloud because it becomes cloudy when immersed in acid. Elaeolite is from a Latin Word for oil because of its greasy luster.
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