Basalt with Plagioclase Feldspar

Physical Properties

Dark gray to black matrix (basalt) with light-colored, whitish to pale greenish patches (plagioclase feldspar). Basalt hardness is ~5-6. Feldspar hardness is ~6. Luster is somewhat dull or earthy on weathered surfaces.

Formation & Geological History

Formed from the rapid cooling of basaltic lava at or near the Earth's surface. The larger feldspar crystals (phenocrysts) began forming deeper in the magma chamber before eruption.

Uses & Applications

Primarily used as crushed stone for construction, road base, asphalt, and concrete aggregates. Has minimal collecting value unless part of a specific formation or containing rare inclusions.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The contrast between the dark matrix and light crystals is a classic example of porphyritic texture.

Field Identification & Locations

Identify by its dark color, fine-grained matrix, and the presence of lighter, blocky crystals. Common in areas with past volcanic activity.

Identified on: 5/20/2026

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