igneous
Porphyritic Basalt
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs. Color: dark gray to black matrix with visible dark phenocrysts. Luster: dull to sub-metallic. Texture: porphyritic (large crystals in fine-grained matrix).
- Hardness
- 5-6 Mohs
- Color
- dark gray to black matrix with visible dark phenocrysts
- Luster
- dull to sub-metallic
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: 5-6 Mohs. Color: dark gray to black matrix with visible dark phenocrysts. Luster: dull to sub-metallic. Texture: porphyritic (large crystals in fine-grained matrix).
Formation & geological history
Formed from the rapid cooling of magnesium and iron-rich lava at or near the Earth's surface. The large crystals (phenocrysts) formed earlier in the magma chamber before the final eruption.
Uses & applications
Used primarily as crushed stone for aggregate in construction, road base, and railroad ballast. Compact specimens are sometimes used as building stone or for garden landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark, dense matrix and visible crystal inclusions. Commonly found in volcanic fields, oceanic islands (like Hawaii), and mid-ocean ridges.
