Basalt (with possible iron oxide staining)

Physical Properties

Hardness: 6-7 Mohs; Color: Dark grey to black, with brownish-orange oxidation; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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. This specimen shows weathering and oxidation (limonite/hematite staining) which suggests exposure to water and air over a significant geological period.

Uses & Applications

Used extensively in construction as aggregate, road base, and railroad ballast. Dense varieties are used for high-quality floor tiles and monuments.

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

Identify in the field by its dark color, heavy weight for its size, and absence of visible large crystals. Often found near volcanic regions or ancient rift zones.

Identified on: 5/7/2026

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