Basalt with Calcite Veining

Physical Properties

Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white streaks; Luster: Dull/earthy; Structure: Massive to fine-grained; Cleavage: None for basalt; Specific Gravity: 2.8–3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white veins formed later as mineral-rich groundwater deposited calcite into fractures.

Uses & Applications

Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Small specimens are used for teaching geological processes.

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 on the Moon and Mars.

Field Identification & Locations

Identified by its dark color, fine-grained texture, and high density. The white veins will react (fizz) if a drop of weak acid is applied. Found in volcanic regions worldwide.

Identified on: 5/1/2026

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