igneous
Porphyritic granite boulder
Granite, commonly quartz–alkali feldspar–plagioclase with biotite/hornblende
AI-generated identification · may be incorrectCoarse crystalline, light gray to pink matrix with conspicuous red/pink feldspar crystals; vitreous quartz and granular texture, typically Mohs 6–7, no foliation, poor cleavage as a whole, and specific gravity about 2.6–2.7.
Identified More igneous →
Explore Porphyritic granite boulder in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse crystalline, light gray to pink matrix with conspicuous red/pink feldspar crystals; vitreous quartz and granular texture, typically Mohs 6–7, no foliation, poor cleavage as a whole, and specific gravity about 2.6–2.7.
Formation & geological history
An intrusive igneous rock formed by slow cooling of silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic plutonic events; the rounded shape reflects later weathering and transport.
Uses & applications
Used for building stone, curbing, paving, monuments, countertops, and landscaping; attractive feldspar-rich pieces may be collected but usually have modest commercial value.
Geological facts
The red crystals are likely potassium feldspar phenocrysts, while dark grains may be biotite or amphibole. Individual crystals are visible because underground cooling was slow.
Field identification & locations
Identify it by interlocking visible crystals, abundant pale quartz/feldspar, and pink-red feldspar grains; it commonly occurs in continental mountain belts and glacial or stream gravels. Exact classification requires a fresh surface or thin section.
