Phonolite

Aegirine phonolite. Dark prismatic minerals are aegirine phenocrysts.

Phonolite, sometimes known as Clinkstone is an igneous, volcanic (extrusive) rock, of intermediate (between felsic and mafic) composition, with aphanitic to porphyritic texture. Mineral assemblage is usually abundant feldspathoids and alkali feldspar, and lesser plagioclase. Biotite, amphibole and pyroxene are common accessory minerals. Quartz is absent.

Some phonolite outcrops make a musical sound when struck -- hence the name.

See also