Phonolite

Phonolitic rocks are fine-grained felsic igneous rocks lacking quartz, with felsics comprising 10-60% foids and alkali feldspar/total feldspar >0.9. The fine-grained equivalent of nepheline syenite, and may be extrusive or in high level dykes or sills. The principal mineral is anorthoclase or sanidine. Other major minerals may include nepheline, aegirine and diopside, usually with other feldspathoidal minerals such as sodalite or hauyne. Accessories include apatite and titanite.