Basalt (Fieldstone)

Physical Properties

Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull or earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8 - 3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen appears rounded, suggesting it was transported by water or glacial activity as a glacial erratic.

Uses & Applications

Used primarily in construction for road base, concrete aggregate, railroad ballast, and occasionally for stonewalling or landscaping.

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 by its dark color, heavy weight (density), and lack of visible individual crystals. Commonly found in volcanic regions or as 'fieldstone' in glaciated areas.

Identified on: 4/14/2026

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