igneous
Greenstone Porphyry
Porphyritic Metavolcanic Rock
Hardness: 6-7 (Mohs); Color: Dark green matrix with greenish-white or pinkish feldspar phenocrysts; Luster: Dull to sub-vitreous; Structure: Massive with porphyritic texture; Cleavage: None (conchoidal fracture).
- Hardness
- 6-7 (Mohs)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark green matrix with greenish-white or pinkish feldspar phenocrysts; Luster: Dull to sub-vitreous; Structure: Massive with porphyritic texture; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from volcanic eruptions where magma cooled at two different rates, creating large crystals (phenocrysts) in a fine-grained matrix. Often metamorphosed over millions of years (Greenschist facies), common in Precambrian and Paleozoic terrains.
Uses & applications
Used as high-quality building stone, decorative landscaping, and historically for stone tools due to toughness. Occasionally used in jewelry as 'Green Porphyry'.
Geological facts
The 'Green Porphyry' specifically from Greece (Lapis Lacedaemonius) was highly prized by Roman emperors and used in the Pantheon and the Church of Hagia Sophia.
Field identification & locations
Identify by the distinct 'spotted' appearance of large crystals embedded in a uniform green background. Often found as rounded river stones or glacial erratics in the Northern US and Europe.
