Basalt with Scoria

Physical Properties

Hardness: 5-6 (Mohs scale); color: dark grey, brownish-red (oxidation); luster: dull to earthy; texture: fine-grained (aphanitic) with vesicular/porous regions; cleavage: none; specific gravity: 2.8 - 3.0.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. The porous (vesicular) reddish section indicates gas bubbles trapped during cooling and subsequent oxidation of iron minerals. These rocks can range from recent volcanic activity to billions of years old.

Uses & Applications

Used in construction as aggregate for roads, railroad ballast, and in the production of stone wool insulation. Occasionally used in landscaping or as aquarium stone.

Geological Facts

Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. It is also the primary volcanic rock on the Moon and Mars.

Field Identification & Locations

Identify by its heavy weight (density), dark color, and fine-grained texture. Reddish-brown crusting often indicates weathering or high iron content. Common in volcanic regions like the Pacific Northwest, Hawaii, and Iceland.

Identified on: 4/19/2026

Mode: Standard