Phonolite

phonolite

[′fō·nə‚līt]

(petrology)

A light-colored, aphanitic rock of volcanic origin, composed largely of alkali feldspar, feldspathoids, and smaller amounts of mafic minerals.

Phonolite

 

(from the Greek phone,”sound,” and lithos,”stone”), the extrusive equivalent of nepheline syenite. Phonolite consists of feldspathoids (nepheline and other rocks), sanidine, and chromatic minerals (alkaline pyroxene and amphibole). It often contains phenocrysts of hauynite, noselite, and, sometimes, plagioclase. Its texture is usually porphyritic. The cleavage is laminar; individual plates of phonolite ring strongly when struck with a hammer (hence the name). Phonolite is used as gravel in road paving and as an aggregate for concrete.