igneous
Porphyry
Porphyritic igneous rock
AI-generated identification · may be incorrectHardness: 6-7. Color: Dark green to black matrix with white phenocrysts. Luster: Dull to subvitreous. Texture: Porphyritic (large crystals in a fine-grained matrix).
- Hardness
- 6-7
- Color
- Dark green to black matrix with white phenocrysts
- Luster
- Dull to subvitreous
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Physical properties
Hardness: 6-7. Color: Dark green to black matrix with white phenocrysts. Luster: Dull to subvitreous. Texture: Porphyritic (large crystals in a fine-grained matrix).
Formation & geological history
Formed from magma that cooled in two stages: slow cooling deep underground to form large crystals (phenocrysts), followed by rapid cooling near the surface to form the fine-grained matrix.
Uses & applications
Used historically and currently as a decorative building stone, in monuments, and for architectural facing due to its striking appearance and durability.
Geological facts
The term 'porphyry' originally referred to a specific purple-red rock from Egypt, but is now used structurally for any igneous rock with this specific texture.
Field identification & locations
Identified by the distinct contrast in crystal sizes; large, visible crystals scattered within a fine-grained or glassy groundmass. Common in volcanic regions worldwide.
