Feldspathoid

Short description: Mineral grouping of silica-poor tectosilicates

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, and are usually not found in rocks containing primary quartz. A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite.[1]

Foid, a 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 nepheline-bearing syenite or nepheline syenite, with the term nepheline replaceable by any foid mineral. Such terminology is used in the Streckeisen (QAPF) classification of igneous rocks.[2]

## Feldspathoid minerals

* Chemistry:Afghanite
* Chemistry:Analcime - Tectosilicate mineral
* Chemistry:Cancrinite - Feldspathoid mineral
* Chemistry:Kalsilite
* Chemistry:Leucite
* Chemistry:Nepheline
* Chemistry:Petalite
* Sodalite Group
* Chemistry:Hauyne
* Chemistry:Lazurite
* Chemistry:Nosean
* Chemistry:Sodalite
* Chemistry:Tugtupite

## References

1. ↑ "The Feldspathoid Group of Minerals". Amethyst Galleries, Inc.. http://www.galleries.com/minerals/silicate/feldspat.htm.
2. ↑ Allaby, Ailsa; Allaby, Michael (1999). A Dictionary of Earth Sciences. Oxford University Press.

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