igneous
Porphyritic Granite pebble (or Porphyry)
Porphyritic Plutonic Igneous Rock (Granite / Monzonite porphyry)
Hardness: 6-7 on Mohs scale. Color: Dark gray to black matrix with distinct pinkish-orange orthoclase feldspar phenocrysts and glassy quartz grains. Luster: Dull to vitreous. Structure: Phaneritic to porphyritic texture (large crystals embedded in a fine to medium-grained matrix).
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous
Identified More igneous →
Explore Porphyritic Granite pebble (or Porphyry) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark gray to black matrix with distinct pinkish-orange orthoclase feldspar phenocrysts and glassy quartz grains. Luster: Dull to vitreous. Structure: Phaneritic to porphyritic texture (large crystals embedded in a fine to medium-grained matrix).
Formation & geological history
Formed via a two-stage cooling process of silica-rich magma. The large feldspar crystals (phenocrysts) grew slowly deep underground, while the surrounding darker matrix cooled more rapidly as the magma migrated higher in the crust.
Uses & applications
Commonly used as construction aggregate, decorative landscaping stone, dimension stone (when in large slabs), and for lapidary tumbling and rock collecting.
Geological facts
Porphyritic rocks record a dynamic volcanic or plutonic history, showing how magma cooling rates changed over time before the rock fully solidified.
Field identification & locations
Identified by the prominent, distinctly shaped pink alkali feldspar crystals suspended in a darker, finer-grained mineral matrix. Very common in glacial till, riverbeds, and gravel deposits worldwide.
