- nepheline syenite
Medium-to coarse-grained igneous rock, a member of the alkali-syenite group, which consists largely of feldspar and nepheline.Nepheline syenite from Canada is used to replace feldspar in the manufacture of ceramic and glass products.
* * *▪ rockmedium- to coarse-grained intrusive igneous rock, a member of the alkali-syenite group (see syenite) that consists largely of feldspar and nepheline. It is always considerably poorer in silica and richer in alkalies than granite. The extraordinarily varied mineralogy of the nepheline syenites and their remarkable variation in habit, fabric, appearance, and composition have attracted much attention; more petrographic research has been devoted to them than to any other plutonic rock. Nepheline syenite from Canada is used to replace feldspar in the manufacture of ceramic and glass products.The feldspar in nepheline syenite may be cryptoperthite or, rarely, a mixture of albite and microcline. Nepheline is sometimes wholly or partly replaced by sodalite or cancrinite. The commonest dark silicate is green pyroxene; and alkaline amphibole (green, brown, or blue) is also abundant. In some areas pyroxene is virtually absent, and it is replaced by a mixture of hornblende and biotite. Rocks that contain more than 30 percent (by volume) of either dark silicates or nepheline usually are not called nepheline syenite. Quartz and calcium-rich plagioclase feldspar are absent, but calcite is almost never absent and may be abundant. Minerals rich in zirconium, titanium, and rare earths occur frequently and sometimes in great abundance.The amount of nepheline syenite and related volcanic or plutonic rocks in the lithosphere is very small, yet they occur in great variety on every major landmass, and volcanic representatives are known from a considerable number of oceanic islands. Plutonic nepheline rocks ordinarily occur in small complexes, some quite isolated, but most in close association with effusive rocks of similar composition.
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Nepheline syenite — of the Intrusive Complex of Tanguá, State of Rio de Janeiro, Brasil (Motoki et al., 2011a) Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or… … Wikipedia
nepheline syenite — nefelino sienitas statusas T sritis chemija apibrėžtis Magminė uoliena, susidedanti iš šarminių feldšpatų (65–70%), nefelino (nepheline syenite 20%) ir nedidelio kiekio biotito, piroksenų, amfibolų. atitikmenys: angl. nepheline syenite rus.… … Chemijos terminų aiškinamasis žodynas
nepheline-syenite — … Useful english dictionary
Syenite — is a coarse grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts ( … Wikipedia
Nepheline — General Category Silicate mineral Chemical formula (Na,K)AlSiO4 … Wikipedia
syenite — syenitic /suy euh nit ik/, adj. /suy euh nuyt /, n. a granular igneous rock consisting chiefly of orthoclase and oligoclase with hornblende, biotite, or augite. [1790 1800; < L syenites (lapis) (stone) of SYENE < Gk syenítes (líthos); see ITE1] * … Universalium
néphéline — ● néphéline nom féminin Aluminosilicate de sodium du système hexagonal, appartenant au genre feldspathoïde. (La néphéline se forme dans les roches magmatiques sous saturées en silice [syénite néphélinique, phonolite].) ⇒NÉPHÉLINE, subst. fém.… … Encyclopédie Universelle
Litchfieldite — is a rare metamorphosed igneous rock. It is a variety of nepheline syenite and is composed of two near pure phases of feldspar, albite and microcline, with predominance of the first one, plus nepheline, sodalite, cancrinite and calcite. The mafic … Wikipedia
Case hardening of rocks — Case hardening is a weathering phenomenon of rock surface induratoin. It is observed commonly in: felsic alkaline rocks, such as nepheline syenite, phonolite and trachyte; pyroclastic rocks, as pyroclastic flow deposit, fine air fall deposits and … Wikipedia
Borolanite — is one of the most remarkable rocks of the British Isles, found on the shores of Loch Borolan in Sutherland shire, after which it has been named. In this locality there is a considerable area of granite rich in red alkali feldspar, and passing,… … Wikipedia