A fine-grained, porphyritic, extrusive, igneous rock consisting of essential alkali feldspar (sanidine or anorthoclase), nepheline, sodic pyroxene, and sodic amphibole (with or without iron-rich olivine), with accessory sphene, apatite, and zircon. Where present, phenocrysts can consist of alkali feldspar, sodic pyroxene, or sodic amphibole. Phonolites are the extrusive equivalent of nepheline-syenites and are found on off-axis ocean islands and in continental regions subjected to anorogenic upwarping and rifting. The name, from the Greek phone meaning ‘sound’, refers to the fact that the rock rings like a bell when struck with a hammer.