Basalt (River-worn Specimen)

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal grey; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); 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 particular specimen shows rounded edges indicating water erosion in a river or coastal environment, a process occurring over hundreds to thousands of years.

Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and high-quality asphalt. In specialized forms, it is used for stone wool insulation or in dimensional stone for 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 on the Moon, Mars, and Venus.

Identify by its heavy weight (high density), dark color, and lack of visible individual crystals without a lens. Often found in volcanic regions or in riverbeds downstream from volcanic sources. Collectors look for unique wear patterns or vesicles (gas bubbles), though this specimen is solid and water-worn.