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The Mineral nepheline

Blocky Nepheline Crystals

Nepheline is a rock-forming mineral. It is usually massive and in unattractive specimens, though a handful of localities have produced well-crystallized examples of this mineral. Nepeheline is a primary constituent of nepheline syenite rocks and nepheline syenite pegmatites, forming in alkali-rich plutonic environments often together with a host of rare minerals.

Chemical Formula

(Na,K)AlSiO4

Color

Colorless, white, gray, cream, yellow, brown

Crystal System

Hexagonal

Properties

Streak
White
Hardness
5.5 - 6
Transparency
Transparent to opaque
Specific Gravity
2.5 - 2.6
Luster
Vitreous to greasy
Cleavage
2,3
Fracture
Subconchoidal to uneven
Tenacity
Brittle

Crystal Habits

Crystals, which are uncommon, are prismatic, stout or tabular, and usually have a good hexagonal shape with a flattened termination. Crystals are often intergrown or stacked. Nepheline is most often massive or grainy.

3D Crystal Atlas

Additional Information

Composition
Sodium potassium aluminum silicate
In Group
Silicates; Tectosilicates; Feldspathoid Group
Striking Features
Environment, greasy luster, and cleavage
Environment
In alkaline igneous nepheline syenites and nepheline syenite pegmatites.
Rock Type
Igneous

Other Names

Elaeolite Obsolete synonym of Nepheline.

Uses

Nepheline is used in the production of glass and ceramics.

Noteworthy Localities

Though massive Nepheline can be found in many locations, good examples of this mineral are only found in a handful of places. Nepheline with a brilliant blue coating of Nosean-impregnated Sodalite comes from Sar-e-Sang, Kochka Valley, Badakshan Province, Afghanistan. Some of the best crystals of Nepheline, in white and gray prismatic crystal clusters, are found in Bou Agrao Mt., Khénifra Province, Morocco. Excellent white and colorless crystals were found in Italy at Monte Somma, Vesuvius; and in several areas around Rome area. Microscopic colorless Nepheline crystals come from Üdersdorf, Hillesheim, and Ettrigen, in the Eifel Mountains of Germany.

In Canada, large, well-formed Nepheline crystals occur in Hastings Co., Ontario, in both Bancroft and at Dungannon Township (at Davis Hill). Small gray crystals came from Mont Saint Hilaire, Quebec. In the U.S., rough Nepheline masses come from Litchfield, Kennebec Co., Maine; and small crystals were found in Magnet Cove, Hot Spring County, Arkansas.

Common Mineral Associations

Albite, Apatite, Calcite, Biotite, Sodalite, Hematite, Aegirine, Cancrinite, Sodalite

Distingushing Similar Minerals

Feldspars - Lack greasy luster and have better cleavage.
Scapolite - Different cleavage.

nepheline Photos



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