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 wit...
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http://en.wikipedia.org/wiki/Feldspathoid
any of a group of alkali aluminosilicate minerals similar to the feldspars in chemical composition but either having a lower silica-alkali ratio or ...
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http://www.britannica.com/eb/a-z/f/15
Any of a group of silicate minerals resembling feldspars but containing less silica. Examples are nepheline (NaAlSiO
4 with a little potassium) and leucite (KAlSi
2O
6). Feldspathoids occur in igneous rocks that have relatively high proportions of sodium and potassium. Such rocks may...
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https://www.encyclo.co.uk/local/21221
No exact match found.
