Basalt

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Fine-grained/Aphanitic, Specific gravity: 2.8 - 3.0

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. This specimen appears water-worn, suggesting a secondary environment like a riverbed or coastal area.

Used widely in construction as crushed stone for road bases and railroad ballast. Also used as floor tiles and for industrial-scale cast basalt liners.

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, Mars, and Venus.

Identify by its heavy weight (density) and dark, uniform coloring. Usually lacks visible crystals. Commonly found in volcanic regions or river beds carrying volcanic debris.