Mineralogy
Phonolites, as they are products of low degree partial melts, are silica undersaturated, and have feldspathoids in their normative mineralogy.
Mineral assemblages in phonolite occurrences are usually abundant feldspathoids (nepheline, sodalite, hauyne, leucite and analcite) and alkali feldspar (sanidine, anorthoclase or orthoclase), and rare sodic plagioclase. Biotite, sodium rich amphiboles and pyroxenes along with iron rich olivine are common minor minerals. Accessory phases include titanite, apatite, corundum. zircon, magnetite and ilmenite. Phonolites are silica under-saturated, as illustrated by the position of phonolite in the TAS classification and QAPF diagrams.
Phonolite is a fine-grained equivalent of nepheline syenite, and the genesis of such magmas is discussed in the treatment of that rock type.
Read more about this topic: Phonolite