Gneiss with Quartz Vein

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Banded gray, black, and white; Luster: Vitreous on quartz, dull to pearly on gneiss; Structure: Foliated with crystalline vein; Cleavage: None (conchoidal fracture in quartz).

Formation & Geological History

Formed through high-grade regional metamorphism of igneous or sedimentary protoliths. The quartz vein formed via hydrothermal fluids filling fractures during tectonic activity.

Uses & Applications

Used primarily as crushed stone for road construction, railroad ballast, and occasionally as decorative building stone or 'landscaping rock'.

Geological Facts

Gneiss is one of the oldest rock types on Earth, with some specimens in the Acasta Gneiss complex dating back over 4 billion years. The banding is caused by the segregation of minerals under intense pressure.

Field Identification & Locations

Identify by looking for 'Gneissic banding' (alternating dark and light layers). In the field, look for cross-cutting veins where minerals filled cracks in the host rock. Extremely common in shield areas like Canada or Scandinavia.

Identified on: 4/23/2026

Mode: Standard