Geologists use the term porphyry only with a word in front of it describing the composition of the groundmass. This image, for instance, shows an andesite porphyry. The fine-grained part is andesite and the phenocrysts are light alkali feldspar and dark biotite. Geologists also may call this an andesite with porphyritic texture. That is, "porphyry" refers to a texture, not a composition, just as "satin" refers to a type of fabric rather than the fiber it's made from (see the various igneous rock textures). See other examples of porphyritic texture in the volcanic rocks gallery. A porphyry may be plutonic, intrusive or extrusive.
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Geology and Society