picrite

picrite
/pik"ruyt/, n.
a granular igneous rock composed chiefly of olivine and augite, but containing small amounts of feldspar.
[1805-15; < Gk pikr(ós) bitter + -ITE1]

* * *

rock
      intrusive igneous rock of ultramafic (very silica-poor) composition that is composed largely of olivine and augite and is somewhat similar to peridotite. Picrites are dark, heavy rocks and contain a small but variable amount of plagioclase feldspar; hornblende and biotite may also be present. Picrites usually occur in sills (tabular bodies inserted while molten between other rocks), but, unlike peridotites, they seldom are found in large plutonic masses. Varieties include augite-, enstatite-, and hornblende-picrite. The term picrite-basalt is reserved for feldspar-poor basalts rich in olivine.

      The minerals in picrite are, in many cases, altered. Serpentine partially or wholly replaces olivine, and hornblende, talc, and chlorite appear as secondary products after the mineral. Augite passes into hornblende or chlorite, and the essential feldspar is often represented by epidote, prehnite, and white mica. In some picrites, as in the peridotites, a lustre mottling is produced by the inclusion of unoriented grains of olivine within large crystals of augite or hornblende.

      The augite picrites of Scotland and the Czech Republic contain interstitial analcime and are closely related to the teschenites with which they are associated. Other picrites are more clearly calc-alkaline and are associated with diorites or diabases; the hornblende picrites of Gwynedd and Anglesey, Wales, are of this type. Picrites accompany diabases in the Devonian rocks of the Fichtelgebirge (in Germany) and Nassau, as well as Cornwall and Devon, Eng.

* * *


Universalium. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Picrite — ou océanite du Piton de la Fournaise Une picrite est une roche volcanique noire riche en olivine, et minéraux ferro magnésiens. Les picrites rencontrées dans des îles de point chaud (Hawaï, La Réunion) sont qualifiées d océanites. Les océanites… …   Wikipédia en Français

  • Picrite — Pic rite, n. [From Gr. ? bitter.] (Min.) A dark green igneous rock, consisting largely of chrysolite, with hornblende, augite, biotite, etc. [1913 Webster] …   The Collaborative International Dictionary of English

  • picrite — ● picrite nom féminin Roche magmatique ultrabasique et mélanocrate, riche en minéraux ferromagnésiens (surtout l olivine) …   Encyclopédie Universelle

  • picrite — [pik′rīt΄] n. [Fr: see PICRO & ITE1] a dark, olivine rich igneous rock picritic [pik′rit′ik] adj …   English World dictionary

  • Picrite basalt — or oceanite from the Piton de la Fournaise Picrite basalt, picrobasalt or oceanite[citation needed] is a variety of high magnesium olivine basalt that is very rich in the miner …   Wikipedia

  • Picrite — Strukturformel Allgemeines Name Nitroguanidin Andere Namen NQ Picrit Guanite NIGU …   Deutsch Wikipedia

  • picrite — pic·rite …   English syllables

  • picrite — /ˈpɪkraɪt/ (say pikruyt) noun a granular igneous rock composed chiefly of olivine and augite, but containing small amounts of felspar. {Greek pikros bitter + ite1} …  

  • picrite — ˈpiˌkrīt noun ( s) Etymology: French, from picr + ite 1. : a variety of olivine diabase without feldspar 2. : a variety of often porphyritic peridotite composed of either augite or hornblende and olivine …   Useful english dictionary

  • VOLCANISME ET VOLCANOLOGIE — Le 24 août de l’an 79 après J. C., le Vésuve se réveilla au terme d’un repos de plusieurs siècles et détruisit les villes d’Herculanum, de Pompéi et de Stabiès. En 1783, l’éruption fissurale du Laki, en Islande, entraîna la mort de plus de 10 000 …   Encyclopédie Universelle

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”