igneous
Basalt with Plagioclase Microphenocrysts
Amygdaloidal or Porphyritic Basalt
Hardness: 6 (Mohs); Color: Dark grey to black matrix with white/off-white inclusions; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) with larger macro-crystals; SG: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black matrix with white/off-white inclusions
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black matrix with white/off-white inclusions; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) with larger macro-crystals; SG: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface. The white patches represent secondary mineral infilling or localized zones of plagioclase feldspar crystallization.
Uses & applications
Mainly used as aggregate in construction, road base, and railroad ballast. Larger specimens are of interest to student geologists for Studying volcanic cooling rates.
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 in the field by its heavy weight (high density), dark matrix, and fine-grained texture. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.
