igneous
Porphyritic Granite
Porphyritic Felsic Igneous Rock
Hardness: 6-7 (Mohs), Color: Orange-tan groundmass with white/light gray phenocrysts, Luster: Dull to vitreous, Texture: Porphyritic (large crystals in fine-grained matrix), Specific Gravity: 2.6-2.7
Identified More igneous →
Explore Porphyritic Granite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs), Color: Orange-tan groundmass with white/light gray phenocrysts, Luster: Dull to vitreous, Texture: Porphyritic (large crystals in fine-grained matrix), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the slow cooling of magma deep underground, allowing large crystals (phenocrysts) to form before a more rapid cooling phase solidified the surrounding matrix.
Uses & applications
Used in construction, as aggregate, for decorative stone/facades, and occasionally for high-end countertops or landscaping rocks.
Geological facts
The term porphyry comes from the Ancient Greek word for purple, as the first specimens discovered were deep purple stones from Egypt. This specific specimen shows iron oxide staining (limonite) giving it the orange-yellow hue.
Field identification & locations
Identify by looking for distinct, larger visible crystals of feldspar or quartz set within a more uniform, smaller-grained background. Common in batholiths and mountain ranges.
