igneous
Porphyritic Basalt
Basalt (SiO2 percentage 45-52%) with phenocrysts
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with light-colored crystals; Luster: Dull to sub-vitreous (when wet); Crystal Structure: Aphanitic matrix with visible phenocrysts; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black matrix with light-colored crystals
- Luster
- Dull to sub-vitreous (when wet)
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: 6-7 Mohs; Color: Dark grey to black matrix with light-colored crystals; Luster: Dull to sub-vitreous (when wet); Crystal Structure: Aphanitic matrix with visible phenocrysts; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The distinct spots (phenocrysts) formed earlier in the magma chamber before the final eruption.
Uses & applications
Commonly used as crushed stone for construction, road base, and railroad ballast. Decorative specimens are used in landscaping or as aquarium stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Porphyritic textures indicate a two-stage cooling process for the magma.
Field identification & locations
Identified by its dark, dense heavy matrix peppered with distinct, larger crystal inclusions. Frequently found in volcanic regions, riverbeds, and glacial till.
