Nepheline


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Related to Nepheline: analcime, Cancrinite, leucite, Nepheline syenite

nepheline

[′nef·ə‚lēn]
(mineralogy)
A mineral of variable composition, with its purest state represented by the formula NaAlSiO4; calcium, magnesium, iron (Fe2+and Fe3+), and titanium are usually present in only minor or trace amounts.

Nepheline

 

a mineral of the tectosilicate class with chemical composition KNa3 [AlSiO4]4. It usually contains an excess of Si and admixtures of Ca, Mg, and, more rarely, Fe, Be, Cl, H2O, and Ga. The structure of nepheline is based on a slightly distorted structure of tridymite, whose large holes (spaces) contain alkaline cations. The arrangement of the (Si, Al) tetrahedrons distorts the structure in such a way that it has no plane of symmetry.

Nepheline crystallizes in the hexagonal system to form massive grainy aggregates and, more rarely, small prismatic crystals. It has a hardness of 5.5–6 on Mohs’ scale and a density of 2,550–2,650 kg/m3. The cleavage is imperfect; the luster varies from vitreous to greasy. The mineral is usually colorless, pink, gray, or greenish.

Nepheline is readily soluble in acid, yielding flocculent silica. It is a principal mineral constituent of alkali rocks (nepheline syenites and their pegmatites). Nepheline alters to sodalite, cancrinite, and zeolites upon the action of postmagmatic solutions. Under supergenic conditions, it converts to hydromica, mont-morillonite, and halloysite; lateritic weathering causes nepheline to alter to gibbsite.

In the USSR, major nepheline deposits are located on the Kola Peninsula, in the Il’men’ Mountains (Urals), in Krasnoiarsk Krai, and in the Alai Range. Other deposits are found in Greenland, Norway, Sweden, the Federal Republic of Germany, Kenya, and elsewhere. In the USSR, a process has been developed permitting an efficient utilization of the mineral whereby aluminum, soda, and other products are obtained. Nepheline is also used in glassmaking, in the preparation of silica gel, and in agriculture as a fertilizer for acidic soils.

REFERENCES

Betekhtin, A. G. Kurs mineralogii, 2nd ed. Moscow, 1956.
kostov, I. Mineralogiia. Moscow, 1971. (Translated from English.)

M. D. DORFMAN

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Weathering data is presented here for alkyd latex formulations using both pyrogenic silica and Nepheline Syenite due to its durability under both acid and alkaline conditions.
As K sources, the feldspathoids nepheline and balliranoite and biotite mica could be considered, with high weathering rates of the latter according to the Goldich dissolution series (Goldich, 1938).
Although the unusual rocks near Litchfield, Maine, had been known to mineral collectors for decades prior, Clarke (1886) provided the first detailed mineralogical descriptions of nepheline syenite from the Litchfield pluton.
And it has a refractive index close to that of nepheline syenite, while outperforming talc and DE in terms of clarity, according to its producer.
The decrease in the volume of nepheline mine took place mainly due to the reduced alumina production at Achinsk Alumina Refinery.
The majority of the analyses are characterized by high contents of TiO2 and total alkalis, they contain olivine in the norms, together with nepheline in six.
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The synthetic zeolite pellets are composed by potassium-sodium zeolite type A (ICDD PDF 76-6495), nepheline (ICDD PDF 78-8388) and leucite (1: ICDD PDF 13-2785 and 2: ICDD PDF 06-5428).
Ijolite in turn is a rare type of alkaline rock, consisting mainly of two minerals--augite (a dark green to black sodium-rich pyroxene) and nepheline (a light-coloured sodium- and potassium-rich aluminum silicate).
After exposing the specimen to 900[degrees]C, peaks for hydroxysodalite disappeared and new crystalline phases like nepheline (NaAlSi[O.