Historical reference: Do not rely on this information. It is very old. About this collection
Porphyry, a term signifying literally "purple," the precise limitations of which, as appliecf to certain ornamental stones in ancient times, are uncertain. Modern petrographers prefer to use it rather in an adjectival form as applying to any igneous rock in which one or two minerals occur in large distinct crystals, as, for instance, does the orthoclase felspar in the porphvritic granite of Shap Fell.