Basalt with Porphyritic Texture

Physical Properties

Hardness: 6 (Mohs). Color: Dark grey to black groundmass with light-colored (plagioclase) crystals. Luster: Dull to sub-metallic. Crystal Structure: Aphanitic groundmass with visible phenocrysts. 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. The larger crystals (phenocrysts) formed slowly underground before the lava erupted and cooled quickly.

Uses & Applications

Used primarily in construction for crushed stone, road base, concrete aggregate, and sometimes in decorative landscaping or as industrial pavers.

Geological Facts

Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. Porphyritic textures tell a 'two-stage' cooling story of the magma's history.

Field Identification & Locations

Identify by its dark, dense matrix and the presence of small, lighter rectangular crystals. Commonly found in volcanic regions, riverbeds near volcanic ranges, and oceanic islands.

Identified on: 4/29/2026

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