igneous
Basalt with Quartz/Calcite Inclusion
Aphanitic Mafic Igneous Rock (Basalt) with SiO2 or CaCO3 vein
Hardness: 5-7 Mohs (matrix). Color: Dark grey/greenish matrix with a tan/cream inclusion. Luster: Dull to earthy. Crystal structure: Fine-grained/aphanitic with massive secondary infilling.
- Hardness
- 5-7 Mohs (matrix)
- Color
- Dark grey/greenish matrix with a tan/cream inclusion
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-7 Mohs (matrix). Color: Dark grey/greenish matrix with a tan/cream inclusion. Luster: Dull to earthy. Crystal structure: Fine-grained/aphanitic with massive secondary infilling.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The central light-colored area likely formed via hydrothermal precipitation, where mineral-rich water filled a vesicle (gas bubble) or void in the rock.
Uses & applications
Primarily used as construction aggregate, road base, and in concrete; smaller polished river-worn specimens are used as decorative garden stones or for massage therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large vesicles filled with secondary minerals like this are often called amygdules.
Field identification & locations
Identify in the field by its weight (dense), dark color, and fine-grained texture. Commonly found in volcanic regions, riverbeds, and glacial till. This specific specimen shows significant fluvial tumbling (water-rounding).
