PHONOLITE IS A TYPE OF TRACHYTE (see here) that contains nepheline or leucite rather than quartz. They are commonly fine grained and compact, and split into thin, tough plates, which make a ringing sound when struck, hence the rock’s name. The principal dark-colored mineral is pyroxene, usually in the form of aegirine or augite. Phonolites are common in Europe, especially on the Eifel plateau and the Laacher See, Germany; in the Czech Republic; and in the Mediterranean area, particularly in Italy. In the USA phonolites are found in Colorado, and the Black Hills, South Dakota. The spectacular Devil’s Tower, Wyoming, is probably phonolite’s most famous occurrence (see Trachyte).
- Rock type Intermediate, volcanic, igneous
- Major minerals Sanidine, oligoclase
- Minor minerals Feldspathoids, hornblende, pyroxene, biotite
- Color Medium gray
- Texture Fine to medium, porphyritic