Basalt with Quartz/Feldspar Inclusions

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Dark gray to black matrix with yellowish-tan white bands, Luster: Dull/Earthy (matrix) to Vitreous (vein), Structure: Fine-grained/Aphanitic, Cleavage: None

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava (basalt) at the Earth's surface. The lighter band is likely a secondary hydrothermal mineral deposit, such as quartz or feldspar, that filled a fracture or void in the rock after initial cooling.

Uses & Applications

Primary uses for basalt include road construction, aggregate, and building stone. Specific river-worn specimens like this are primarily used for landscaping or as decorative garden stones.

Geological Facts

The rounding of this specimen indicates it has spent significant time in a high-energy water environment like a river or beach, which smoothed the hard volcanic material over many years.

Field Identification & Locations

Identify in the field by looking for a heavy, dark, fine-grained rock with distinct, lighter mineral veins. It is commonly found in volcanic regions or in glacial outwash plains where rivers carry mountain debris.

Identified on: 4/17/2026

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