igneous
Vesicular Basalt with Magnetite/Hematite
Mafic Extrusive Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 (Mohs); Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Presence of vesicles (gas bubbles).
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black with reddish-brown oxidation
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black with reddish-brown oxidation; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Presence of vesicles (gas bubbles).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The small holes (vesicles) were created by trapped gas escaping during solidification.
Uses & applications
Commonly used as aggregate in construction, road base, railroad ballast, and sometimes in landscaping or as a source of iron ore if concentration is high.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers large areas of the Moon, Mars, and Venus.
Field identification & locations
Identify by its weight (dense for its size), dark color, and small holes (vesicles). Often found in volcanic fields or near ancient lava flows. Test with a magnet for magnetic mineral content.
