Porphyry is a variety of 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. The term
"porphyry" is from Greek and means "purple". Purple was the
color of royalty, and the "Imperial Porphyry" was a deep purple
igneous rock with large crystals of plagioclase. This rock was
prized for various monuments and building projects in Imperial
Rome and later. Subsequently the name was given to igneous rocks
with large crystals. Porphyritic now refers to a texture of
igneous rocks. Its chief characteristic is a large difference
between the size of the tiny matrix crystals and other much
larger phenocrysts. Porphyries may be aphanites or phanerites,
that is, the groundmass may have invisibly small crystals, like
basalt, or the individual crystals of the groundmas