Porphyry is a textural term for an
igneous rock consisting of large-grained
crystals such as
feldspar or
quartz dispersed in a fine-grained
feldspathic matrix or groundmass. The larger crystals are called
phenocrysts. In its non-geologic, traditional use, the term "porphyry" refers to the purple-red form of this stone, valued for its appearance.