Basalt with Scoria

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to vesicular; 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. The vesicular (pitted) portion indicates gas bubbles were trapped during solidification.

Uses & Applications

Used primarily in construction for aggregate, road base, and railroad ballast. Scoria is often used in landscaping and as a high-temperature insulator.

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 crystals. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges. Look for vesicular texture on one side and a denser, smoother texture on the other.

Identified on: 4/29/2026

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