Basalt with Epidote Veining

Physical Properties

Hardness: 6-7 Mohs; Color: Dark grey to charcoal matrix with pale green veins; Luster: Dull/earthy (matrix) to vitreous (veins); Structure: Aphanitic (fine-grained); Specific Gravity: 2.9-3.3

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The green veins are the result of hydrothermal alteration (metasomatism) where hot, mineral-rich fluids infiltrated cracks in the basalt, depositing epidote.

Uses & Applications

Basalt is primarily used as aggregate in construction, road base, and railroad ballast. The epidote-rich varieties are occasionally used for decorative landscaping or by mineral collectors.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The presence of green epidote often indicates low-grade metamorphism, specifically the greenschist facies.

Field Identification & Locations

Identify in the field by its dark, heavy, fine-grained matrix and the presence of characteristic pistachio-green colored veins. Commonly found in volcanic terrains and mid-ocean ridges.

Identified on: 4/22/2026

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