igneous
Basalt (Crushed Roadstone)
Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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's surface. This specimen appears as a part of modern construction aggregate, likely crushed from a volcanic flow deposit.
Uses & applications
Predominantly used as architectural aggregate, road base, concrete reinforcement, and railroad ballast due to its high compressive strength and durability.
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 in abundance on the Moon and Mars.
Field identification & locations
Identify by its heavy weight relative to size, dark gray color, and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in volcanic regions or as imported gravel in driveways/roads.
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Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
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