Basalt (Fieldstone)

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

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.

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

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.

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.