Feldspathoid
Appearance
Thefeldspathoidsare a group oftectosilicatemineralswhich resemblefeldsparsbut have a different structure and much lowersilicacontent. They occur in rare and unusual types ofigneous rocks,and are usually not found in rocks containing primary quartz. A notable exception where feldspathoids and quartz-bearing rocks are found together is theRed Hill Syenite.[1]
Foid,a contraction of the termfeldspathoid,is applied to any igneous rock containing up to 60% modal feldspathoid minerals. For example, asyenitewith significantnephelinepresent can be termed anepheline-bearing syeniteornepheline syenite,with the termnephelinereplaceable by any foid mineral. Such terminology is used in the Streckeisen (QAPF) classification of igneous rocks.[2]
Feldspathoid minerals
[edit]- Afghanite– Tectosilicate mineral
- Analcime– Tectosilicate mineral
- Cancrinite– Feldspathoid mineral
- Kalsilite– Vitreous white to grey feldspathoidal mineral
- Leucite– Potassium and aluminium tectosilicate mineral
- Nepheline– Silica-undersaturated aluminosilicate mineral
- Petalite– Silicate mineral, used in ceramic glazing
- Sodalite Group
- Tugtupite– tectosilicate mineral
References
[edit]- ^"The Feldspathoid Group of Minerals".Amethyst Galleries' Mineral Gallery.Amethyst Galleries, Inc.Retrieved6 Jul2015.
- ^Allaby, Ailsa; Allaby, Michael (1999).A Dictionary of Earth Sciences.Oxford University Press.