(a) any of various kinds of reddish sedimentary rock; a layer or formation consisting of such rock; spec. = red beds n. at compounds 1f(c)(i); (b) Ge…

oriental verd-antique, green porphyry. Occasionally without adjective. Also attributive.

A dark-coloured rock allied to kersantite.

A fine-grained porphyritic compound of oligoclase and mica, containing also hornblende and quartz.

uralite-porphyry, uralite-syenite: (see quots.).

A lamprophyre containing small phenocrysts of olivine and augite, and usually also biotite or an amphibole, in a glassy groundmass consisting of or…

A lamprophyre consisting essentially of phenocrysts of hornblende (or augite) in a groundmass containing potash feldspar.

Any of a group of dark-coloured, usually porphyritic dike-rocks resembling basalt and typically consisting of phenocrysts of hornblende or…

A hypabyssal porphyritic igneous rock having a trachytic texture and consisting essentially of a potash-feldspar with small amounts of pyribole and…

Geology. A porphyritic volcanic rock, usually of a light brown colour, which consists of roughly equal amounts of leucite and ferromagnesian…

Geology. A porphyritic lamprophyre in which the feldspar is sodic plagioclase and the phenocrysts consist of an amphibole or pyroxene, usually green…

A relatively light-coloured, extrusive volcanic rock with a fine-grained porphyritic texture, intermediate in composition between rhyolite and dacite.

Originally: a variety of trachyte, containing quartz. In later use: a typically pale, fine-grained extrusive volcanic rock of granitic…