A big crystal of Nepheline from Canaã Massif, Brazil

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. Image File history File linksMetadata Size of this preview: 800 × 535 pixel Image in higher resolution (1638 × 1095 pixel, file size: 320 KB, MIME type: image/jpeg) Nepheline from the Canaã alkaline massif, Rio de Janeiro, Brazil The mineral surface is lightly wheathered Sample size: 3X2,5 cm Author:Eurico... Image File history File linksMetadata Size of this preview: 800 × 535 pixel Image in higher resolution (1638 × 1095 pixel, file size: 320 KB, MIME type: image/jpeg) Nepheline from the Canaã alkaline massif, Rio de Janeiro, Brazil The mineral surface is lightly wheathered Sample size: 3X2,5 cm Author:Eurico... The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark gray with bluish tinge Atomic mass 28. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Pluton redirects here. ... This article is about volcanoes in geology. ... This article or section does not cite its references or sources. ... For other uses, see Mica (disambiguation). ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ...

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. In materials science, hardness is the characteristic of a solid material expressing its resistance to permanent deformation. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... For the file system called Lustre, see Lustre (file system) Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ...

The low index of refraction and the feeble double refraction in nepheline are nearly the same as in quartz; but since in nepheline the sign of the double refraction is negative, while in quartz it is positive, the two minerals are readily distinguished under the microscope. An important determinative character of nepheline is the ease with which it is decomposed by hydrochloric acid, with separation of gelatinous silica (which may be readily stained by coloring matters) and cubes of salt. For this reason, a clear crystal of nepheline becomes cloudy when immersed in acid. Quartz is one of the most common minerals in the Earths continental crust. ... Robert Hookes microscope (1665) - an engineered device used to study living systems. ... The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride gas (HCl). ... Halite is the mineral form of sodium chloride, NaCl, commonly known as rock salt. ... In databases, ACID stands for Atomicity, Consistency, Isolation, and Durability. ...

Although sodium and potassium are always present in naturally occurring nepheline in approximately the atomic ratio (3:1), artificially prepared crystals have the composition NaAlSiO₄; the corresponding potassium compound, KAISiO₄, which is the mineral kaliophilite, has also been prepared artificially. It has therefore been suggested that the orthosilicate formula, (Na,K)AlSiO₄, represents the true composition of nepheline. General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ...

The mineral is one especially liable to alteration, and in the laboratory various substitution products of nepheline have been prepared. In nature it is frequently altered to zeolites (especially natrolite), sodalite, kaolin, or compact muscovite. Gieseckite and liebenerite are pseudomorphs. Zeolite The micro-porous molecular structure of a zeolite, ZSM-5 Zeolites (Greek, zein,to boil;lithos,a stone) are minerals that have a micro-porous structure. ... Kaolin Kaolinite (Aluminium Silicate Hydroxide) Kaolinite is a mineral with the chemical composition Al2Si2O5(OH)4. ... Muscovite layer Muscovite, also known as potash mica, is a phyllosilicate mineral of aluminium and potassium with formula: KAl2(AlSi3O10)(F,OH)2. ...

Two varieties of nepheline are distinguished, differing in their external appearance and in their mode of occurrence, being analogous in these respects to sanidine or glassy orthoclase and common orthoclase respectively. Glassy nepheline has the form of small, colorless, transparent crystals and grains with a vitreous luster. It is characteristic of the later volcanic rocks rich in alkalis, such as phonolite, nepheline-basalt, leucitebasalt, etc., and also of certain dike-rocks, such as tinguaite. The best crystals are those which occur with mica, sanidine, garnet, etc., in the crystal-lined cavities of the ejected blocks of Monte Somma, Vesuvius. The other variety, known as elaeolite, occurs as large, rough crystals, or more often as irregular masses, which have a greasy luster and are opaque, or at most translucent, with a reddish, greenish, brownish or grey color. It forms an essential constituent of certain alkaline plutonic rocks of the nepheline syenite series, which are typically developed in southern Norway. Orthoclase (KAlSi3O8) is an important tectosilicate mineral, which forms igneous rock. ... Phonolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... A dike in geology refers to a tabular intrusive igneous body. ... For other uses, see Mica (disambiguation). ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Mount Vesuvius (Italian: Monte Vesuvio) is a volcano east of Naples, Italy, located at 40°49′N 14°26′ E. It is the only active volcano on the European mainland, although it is not currently erupting. ... Pluton redirects here. ... Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. ...

The color and greasy luster of elaeolite (a name given by M. H. Klaproth 1809, from Greek words for oil and stone; German Fettstein) are due to the presence of numerous microscopic enclosures of other minerals, possibly augite or hornblende. These enclosures sometimes give rise to a chatoyant effect like that of cats-eye and cymophane; and elaeolite when of a good green or red color and showing a distinct band of light is sometimes cut as a gem-stone with a convex surface. Augite is a mineral described chemically as (Ca, Na)(Mg, Fe, Al)(Al, Si)2O6 or calcium sodium magnesium iron aluminium silicate. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ...

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.