igneous
Red Porphyry (Imperial Porphyry)
Andesite/Dacite Porphyry
AI-generated identification · may be incorrectHardness: 6 - 7 on the Mohs scale; Color: deep reddish-brown to purplish-red fine-grained matrix containing distinctive pale cream to light green phenocrysts; Luster: vitreous to dull (waxy to vitreous when polished); Texture: porphyritic; Specific Gravity: approximately 2.6 - 2.8.
- Hardness
- 6 - 7 on the Mohs scale
- Luster
- vitreous to dull (waxy to vitreous when polished)
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Physical properties
Hardness: 6 - 7 on the Mohs scale; Color: deep reddish-brown to purplish-red fine-grained matrix containing distinctive pale cream to light green phenocrysts; Luster: vitreous to dull (waxy to vitreous when polished); Texture: porphyritic; Specific Gravity: approximately 2.6 - 2.8.
Formation & geological history
Formed via a two-stage cooling process of intermediate to felsic volcanic or hypabyssal magma. Slow cooling deep underground allowed large feldspar phenocryst crystals to grow, followed by rapid cooling nearer the surface which created the fine-grained reddish hematite-rich groundmass.
Uses & applications
Popular for decorative carvings, polished eggs/spheres, cabochons, and ornamental stonework. Historically prized by Roman emperors and Byzantine royalty as an imperial building and sculptural stone.
Geological facts
Ancient Romans called this rock 'porphyrites' (from the Greek for purple) and quarried it at Mons Porphyrites (Gebel Dokhan) in Egypt. Because purple was the color of royalty, it was reserved almost exclusively for imperial busts, columns, and sarcophagi.
Field identification & locations
Identified in the field by large, visible, angular-to-subhedral feldspar crystals (phenocrysts) set within a very fine-grained (aphanitic) reddish or purplish volcanic matrix. Found in Egypt, Sweden, Greece, Australia, and various regions of North America.
