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]

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      any of a class of intrusive igneous rocks essentially composed of an alkali feldspar and a ferromagnesian mineral. A special group of alkali syenites is characterized by the presence of a feldspathoid mineral such as nepheline, leucite, cancrinite, or sodalite (see nepheline syenite). Chemically, syenites contain a moderate amount of silica, relatively large amounts of alkalies, and alumina. The name was first used by Pliny the Elder.

      The texture of syenites, like that of granite, is granular, and these rocks differ from granite only by the absence or scarcity of quartz. The alkali feldspars present may include orthoclase, perthite, albite, or, more rarely, microcline; the ferromagnesian mineral may be biotite, hornblende, or pyroxene. In the alkali syenites, the amphiboles or pyroxenes frequently contain sodium. The more normal syenites are divisible according to their prevalent dark-coloured mineral into augite-, hornblende-, and biotite-syenites; but, like granites, syenites are also divisible according to the type of alkali feldspar into potash and soda syenites. The accessory constituents include titanite, apatite, zircon, magnetite, and pyrites. Syenites are much less common than granites and diorites. The rocks known as nordmarkite and pulaskite are soda syenites. Rocks transitional between syenites and diorites are known as monzonites (monzonite).

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Universalium. 2010.

Look at other dictionaries:

  • 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

  • syénite — [ sjenit ] n. f. • 1765; siémite 1611; lat. syenites, gr. suênitês « de Syène », a. nom d Assouan ♦ Minér. Roche plutonique grenue, composée essentiellement de feldspath alcalin, d un peu de biotite et de hornblende, de couleur blanche, rosée ou… …   Encyclopédie Universelle

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  • Syenite — Sy e*nite, n. [L. Syenites (sc. lapis), from Syene, Gr. ?.] (Min.) (a) Orig., a rock composed of quartz, hornblende, and feldspar, anciently quarried at Syene, in Upper Egypt, and now called {granite}. (b) A granular, crystalline, ingeous rock… …   The Collaborative International Dictionary of English

  • syenite — [sī′ə nīt΄] n. [Fr syénite < L Syenites (lapis), Syenite (stone) < Syene < Gr Syēnē, Syene] a grayish, intrusive igneous rock usually containing feldspar, hornblende, and some quartz syenitic [sī΄ənit′ik] adj …   English World dictionary

  • Syénite — La syénite est une roche magmatique plutonique grenue de couleur rose à rouge. Elle est composée de feldspath alcalin, de biotite et de hornblende. Son nom vient de Syène, ancien nom de la ville d Assouan (Égypte). On peut y ajouter, que l… …   Wikipédia en Français

  • syenite — [ sʌɪənʌɪt] noun Geology a coarse grained grey igneous rock composed typically of alkali feldspar and hornblende. Derivatives syenitic adjective Origin C18: from Fr. syénite, from L. Syenites (lapis) (stone) of Syene , Greek name of Aswan in… …   English new terms dictionary

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  • syenite — noun Etymology: Latin Syenites (lapis) stone of Syene, from Syene, ancient city in Egyptian Date: circa 1796 an igneous rock composed chiefly of feldspar • syenitic adjective …   New Collegiate Dictionary

  • syenite — noun An igneous rock composed of feldspar and hornblende …   Wiktionary

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