noun (plural porphyries)
A hard igneous rock containing crystals, usually of feldspar, in a fine-grained, typically reddish groundmass.
- The fault places massive fractured greenstones over relatively undeformed feldspar andesite porphyry.
- The mine workings occupy much of the west side of an isolated low hill composed mainly of light-colored volcanic rock, described as felsite porphyry or trachyte, highly altered to clay minerals.
- Although closely associated with plutonic igneous rocks, porphyry mineralization commonly encompasses large volumes of the surrounding host rocks to the intrusion.