River Stone (Granitic Gneiss)

Physical Properties

Hardness: 6-7 (Mohs). Color: Speckled gray, tan, and black with rust-colored iron staining. Luster: Dull to waxy when wet. Crystal structure: Phaneritic with slight foliation. Composition: Quartz, Feldspar, and Mica.

Formation & Geological History

Formed through the high-grade metamorphism of igneous rock (granite) or sedimentary rocks under intense heat and pressure deep in the Earth's crust. This specific specimen has been tumbled and rounded by water action in a river or beach environment.

Uses & Applications

Commonly used as decorative landscaping rock, aquarium gravel, or crushed stone for construction and road bases.

Geological Facts

Gneiss is one of the oldest types of rock found on Earth, with some specimens dating back 4 billion years. The banding or speckling results from the segregation of different mineral types during metamorphic processes.

Field Identification & Locations

Identify by its alternating light and dark mineral grains and its extreme hardness. It won't easily scratch with a steel blade. Commonly found in riverbeds, glacial deposits, and mountainous regions.

Identified on: 4/21/2026

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