igneous
Basalt Pebble with Epidote/Olivine
Vitreous Basalt (SiO2 with Ca/Mg/Fe silicates)
Hardness: 6-7 Mohs; Color: Dark grey to black with green/yellow inclusions; Luster: Dull/Matte (pebble) to Vitreous (crystalline parts); Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black with green/yellow inclusions
- Luster
- Dull/Matte (pebble) to Vitreous (crystalline parts)
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black with green/yellow inclusions; Luster: Dull/Matte (pebble) to Vitreous (crystalline parts); Structure: Fine-grained/Aphanitic; Specific Gravity: 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 Earth surface. This specific specimen has been rounded by fluvial (river) or glacial transport processes which smoothed its edges.
Uses & applications
Common basalt is used in construction aggregate, road base, and railroad ballast. Small water-worn pebbles are popular for decorative landscaping, 'worry stones,' and aquarium substrate.
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 extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark weight and fine grain; it will not scratch with a copper penny but can be scratched by a steel file. Commonly found in volcanic regions, riverbeds, and glacial till. This specimen shows 'weathering rinds' where minerals are oxidizing.
