Sedimentary rock with quartz veining

Physical Properties

Hardness: 3-4 (matrix), 7 (veins); Color: Gray to blue-gray with white or tan banding; Luster: Dull to earthy; structure: fine-grained clastic with secondary mineralization.

Formation & Geological History

Formed from the lithification of fine-grained sediment (silt or clay) in a low-energy aquatic environment. The parallel bands (veins) formed later when mineral-rich fluids (likely silica) filled fractures in the rock, a process often associated with tectonic stress.

Uses & Applications

Primarily of geological interest; common field rocks are sometimes used in landscaping, road fill, or as decorative garden stones.

Geological Facts

This specimen is a classic example of 'cross-cutting relationships' in geology—the white veins are younger than the gray rock they penetrate. Such rocks are common in areas that have undergone historical mountain building.

Field Identification & Locations

Identify in the field by checking for harder, raised white lines crossing the softer darker rock. Often found in riverbeds, glacial till, or ancient lake deposits.

Identified on: 4/16/2026

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