Minerals identify

Know how to recognize them



The feldspathoids are a group of tectosilicate 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 present can be termed a '(nepheline)-bearing syenite', or a '(nepheline)-syenite', with the term (nepheline) replaceable by any 'foid' mineral. Such terminology is used in the Streckeisen (QAPF