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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.

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/nepheline syenite, with the term nepheline replaceable 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

References※

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