The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks.

Foid, contraction of the term feldspathoid, is applied to any igneous rock containing up to 60% modal feldspathoid minerals. For example, a syenite with significant nepheline present can be termed a ‘foid-bearing syenite’, or a ‘foid-syenite’. Such terminology is used on the Streckeisen (QAPF) classification of igneous rocks. [A Dictionary of Earth Sciences, Ailsa Allaby and Michael Allaby, Oxford University Press 1999]

Feldspathoid Minerals



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  • feldspathoid — /feld spa thoyd , fel /, Mineral. adj. 1. Also, feldspathoidal. of or pertaining to a group of minerals similar in chemical composition to certain feldspars except for a lower silica content. n. 2. a mineral of this group, as nepheline. [1895… …   Universalium

  • feldspathoid — 1. noun Any of a small group of igneous, plutonic, and volcanic minerals formed in magma that did not contain enough silica to satisfy all the chemical bonds. Feldspathoids are silica poor variants of the feldspar group. ,Varieties: , leucite ,… …   Wiktionary

  • feldspathoid — feld·spath·oid …   English syllables

  • feldspathoid — feld•spath•oid [[t]ˈfɛld spæˌθɔɪd, ˈfɛl [/t]] adj. 1) mir Also, feld spath•oi′dal. of or pertaining to a group of minerals similar in chemical composition to certain feldspars except for a lower silica content 2) mir a mineral of this group, as… …   From formal English to slang

  • feldspathoid — …   Useful english dictionary

  • nepheline — /nef euh lin/, n. a feldspathoid mineral, essentially sodium aluminum silicate, NaAlSiO4, occurring in alkali rich volcanic rocks. Also, nephelite /nef euh luyt /. [1805 15; < F néphéline, equiv. to néphél ( < Gk nephéle cloud) + ine INE2] * * *… …   Universalium

  • Silicate minerals — ▪ Table Silicate minerals name colour lustre Mohs hardness specific gravity Tectosilicates (three dimensional networks) feldspar (for other examples, see feldspar) orthoclase flesh red, white to pale yellow, red, green vitreous 6–6½ 2.6… …   Universalium

  • 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

  • Nosean — crystal group from Ochtendung, Eifel, Germany General Category Sodalite (Feldspathoid) …   Wikipedia

  • analcime — [ə nal′sīt΄ə nal′sīm΄, ə nal′sēm΄] n. 〚< Gr an , not + alkoimos, strong: so named from its weak electricity when rubbed〛 a hard, colorless or white zeolite, NaAlSi2O6·H2O, commonly found in basalts: sometimes called analcite [ə nal′sīt΄] * * *… …   Universalium

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