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[Chemical Composition] The chemical composition of nepheline is an intermediate product of the Na[A1SiO 4 ]-K[AlSiO 4 ] series, in which the K[AlSiO 4 ] molecule is 5% to 20%. Fe 3+ is considered to be a tetrahedral Al 3+ . 
[Crystal structure] hexagonal crystal system; a 0 = 1.00 nm, c 0 = 0.841 nm; Z = 2. The structure of nepheline is similar to that of β-scale quartz , and their c 0 values ​​are similar. The a 0 value of nepheline is twice the value of β scale quartz a 0 . The β-scale quartz is replaced by Al, and the structure of nepheline is formed. Alkali metal appears to be to balance the charge. As a result of the displacement, the structure is inevitably deformed, so that two different forms of six-rings appear in the structure.
[Form] The crystal is often hexagonal or thick plate. It is often a twin crystal that looks like a single crystal. There may also be a granular or dense block assembly (Fig. G-55).
Figure G-55 Nepheline crystal
[Physical properties] often colorless, white, gray or micro-belts of various colors; streaks are colorless or white; transparent, turbid seems to be opaque; glass luster, fractures have obvious oily luster, so it is called "lipid stone" "; streaks are colorless or white. The cleavage is not developed; it has a shell-like fracture. Crisp. Hardness 5 to 6. The relative density is 2.55 to 2.66.
[genesis and occurrence] Nepheline is produced in alkaline rocks lacking SiO 2 rich in Na 2 O , mainly found in intrusive rocks, volcanic rocks and pegmatites associated with syenite. It is formed under the condition that SiO 2 is unsaturated, so in the same rock, nepheline and quartz cannot appear at the same time. The symbiotic minerals are sodium-rich alkaline feldspar (potassium plagioclase, albite), basic pyroxene, basic hornblende and the like.
[identification characteristics] Fresh nepheline produced in rocks is not easily recognized by the naked eye, sometimes like alkaline feldspar, sometimes like quartz.
Very confusing. However, nepheline often has a lustrous luster and no good cleavage, which can be distinguished from feldspar. Nepheline often contains some stained spots, which are easier to weather. If it is found that there are variegated alterations around the particles or in the cracks, it is often nepheline instead of quartz. In addition, if the nepheline powder is placed in a test tube and concentrated with HCl for a few minutes, a gelatinous substance will appear in the residue, which may be distinguished from the quartz.
[Uses] as glass, ceramic industrial raw material, instead of aluminum ore.
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