Feldspathoid

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.

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.

Feldspathoid minerals

• 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
  • Hauyne– Silicate mineral
  • Lazurite– Alumino-silicate mineral whose blue colour is due to a sulfide species and not copper
  • Nosean– tectosilicate mineralPages displaying wikidata descriptions as a fallback
  • Sodalite– Blue tectosilicate mineral
• Tugtupite– tectosilicate mineralPages displaying wikidata descriptions as a fallback