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| Nepheline from Kola Peninsula |
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More Nepheline on ebay auction |
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Nepheline en.wikipedia.org Nepheline, also called nephelite (from Greek: nephos, "cloud"), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is very occasionally found in mica schist and gneiss. Nepheline crystals are rare and belong to the hexagonal system, usually having the form of a short, six-sided prism terminated by the basal plane. The unsymmetrical etched figures produced artificially on the prism faces indicate, however, that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis. It is found in compact, granular aggregates, and can be white, yellow, gray, green, or even reddish (in the eleolite variety). The hardness is 5.5 - 6, and the specific gravity 2.56 - 2.66. It is often translucent with a greasy luster. http://www.galleries.com Nepheline is a member of the feldspathoid group of minerals. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica (SiO2) content, are called feldspathoids. As a result or more correctly as a function of the fact, they are found in silica poor rocks containing other silica poor minerals and no quartz. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar. Localities that have feldspathoids are few. Nepheline is reactive to acids although it does not bubble like many of the carbonates. If powdered it will dissolve in hydrochloric acid and if clear specimens are dipped in acid they will become cloudy or frosted. This could be helpful in distinguishing nepheline from some similar looking feldspars, scapolite and cryolite. http://www.nephelinesyenite.com Nepheline Syenite is a rare igneous rock that, although resembling medium-grained granite in texture, consists principally of nepheline and alkali feldspars. The name sounds ominous but the mineral is not related to cyanide, nor is it poisonous. In fact, Nepheline Syenite is a very beneficial element. It is a "Swiss Army Knife" mineral whose usefulness keeps expanding. |
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