igneous
Porphyritic Basalt
Porphyritic Basalt (Silicate Rock)
Hardness: 6 (Mohs scale); Color: Dark brown to black groundmass with light brown or tan phenocrysts; Luster: Dull to sub-vitreous; Structure: Aphanitic groundmass with visible crystals (porphyritic); Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Luster
- Dull to sub-vitreous
Identified More igneous →
Explore Porphyritic Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale); Color: Dark brown to black groundmass with light brown or tan phenocrysts; Luster: Dull to sub-vitreous; Structure: Aphanitic groundmass with visible crystals (porphyritic); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The larger spots (phenocrysts) formed during a slower cooling phase deep underground before eruption.
Uses & applications
Commonly used as river stones for decoration, landscaping, massage stones (due to heat retention), and as high-quality aggregate in construction.
Geological facts
Often called 'flower stones' when the phenocryst clusters resemble floral patterns. These rounded forms are typically shaped by long-term water erosion in riverbeds.
Field identification & locations
Identified by the distinct contrast between the dark, fine-grained base and the larger, lighter mineral inclusions. Commonly found in volcanic regions or river deposits originating from such areas.
