Aplite


Aplite

Aplite (pronEng|ˈæplaɪt) in petrology, the name given to intrusive rock in which quartz and feldspar are the dominant minerals. Aplites are usually very fine-grained, white, grey or pinkish, and their constituents are visible only with the help of a magnifying lens. Dykes and threads of aplite are commonly observed traversing granitic bosses; they occur also, though less frequently, in syenites, diorites, quartz-diabases and gabbros.

Aplites usually have a genetic affinity to the rocks they intersect. The aplites of granite areas, for example, are the last part of the magma to crystallize, and correspond in composition to the quartzo-feldspathic aggregates that fill up the interspaces between the early minerals in the main body of the rock. They bear a considerable resemblance to the eutectic mixtures which are formed on the cooling of solutions of mineral salts, and remain liquid till the excess of either of the components has separated out, finally solidifying "en masse" when the proper proportions of the constituents and a suitable temperature are reached.

The essential components of aplites are quartz and alkali feldspar (the latter usually orthoclase or microperthite), microcline and albite. Crystallization has been apparently rapid (as the rocks are so fine-grained), and the ingredients have solidified almost at the same time. Hence their crystals are rather imperfect and fit closely to one another in a sort of fine mosaic of nearly equi-dimensional grains. Porphyritic feldspars occur occasionally and quartz more seldom; but the relation of the aplites to quartz-porphyries, granophyres and felsites is very close, as all these rocks have nearly the same chemical composition.

The aplites associated with diorites and quartz-diabases differ in minor respects from the common aplites which accompany granites. The accessory minerals of these rocks are principally oligoclase, muscovite, apatite and zircon. Biotite and all ferromagnesian minerals rarely appear in them, and never in considerable amounts. Riebeckite-granites have close affinities to aplites, shown especially in the prevalence of alkali feldspars. Tourmaline also occurs in some aplites.

The rocks of this group are very frequent in all areas where masses of granite are known. They form dykes and irregular veins which may be only a few inches or many feet in diameter. Less frequently aplite forms stocks or bosses, or occupies the edges or irregular portions of the interior of outcrops of granite. The syenite-aplites consist mainly of alkali feldspar; the diorite-aplites of plagioclase; there are nepheline-bearing aplites which intersect some elaeolite-syenites. In all cases they bear the same relation to the parent masses. By increase of quartz, aplites pass gradually, in a few localities, through highly quartzose modifications into quartz veins.

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Look at other dictionaries:

  • aplite — n. 1. light colored and fine grained granitic rock consisting chiefly of quartz and feldspars. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • aplite — ● aplite nom féminin (grec aploos, simple) Roche magmatique filonienne, à grain fin, hololeucocrate, généralement granitique ou syénitique …   Encyclopédie Universelle

  • aplite — [ap′līt΄] n. [Ger aplit < Gr haploos, simple (see HAPLO ) + ITE1] a light colored, fine grained igneous rock, similar to granite, that often forms in and near dikes, consisting mainly of quartz and feldspar aplitic [ap lit′ik] adj …   English World dictionary

  • Aplite — Filon aplitique d un granodiorite, Železné hory, République tchèque Filons ap …   Wikipédia en Français

  • aplite — aplitic /ap lit ik/, adj. /ap luyt/, n. Petrol. a fine grained granite composed essentially of feldspar and quartz. [1875 80; apl (var. of HAPLO ) + ITE1] * * * or haplite Any igneous rock of simple composition, such as granite composed only of… …   Universalium

  • aplite — aplitas statusas T sritis chemija apibrėžtis Magminė gyslinė smulkiagrūdė uoliena iš kvarco, šarminių feldšpatų, rečiau rūgščių plagioklazų, genetiškai susijusi su abisalinėmis uolienomis. atitikmenys: angl. aplite rus. аплит …   Chemijos terminų aiškinamasis žodynas

  • aplite — noun Etymology: probably from German Aplit, from Greek haploos simple more at hapl Date: 1879 a fine grained light colored granite consisting almost entirely of quartz and feldspar • aplitic adjective …   New Collegiate Dictionary

  • aplite — noun A fine grained granitic rock composed mostly of quartz and feldspars …   Wiktionary

  • aplite — a·plì·te s.f. TS petr. roccia eruttiva a grana finissima di colore chiaro formata essenzialmente da quarzo e feldspati {{line}} {{/line}} DATA: 1875. ETIMO: der. del gr. haplóos semplice con 2 ite …   Dizionario italiano

  • aplite — ap·lite …   English syllables


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