Gneiss

Displaying prominent foliation known as gneissose banding; colors range from gray, white, to tan; hardness 6-7 on Mohs scale; luster is generally dull to sub-vitreous; coarse-grained texture with alternating bands of light and dark minerals.

Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks (like granite or shale) under extreme pressure and temperature. It is often found in the core of mountain ranges and represents deep crustal processes.

Used primarily in the construction industry as crushed stone for road bases and as dimension stone for architectural facings, flooring, curbing, and countertops. It is valued for its durability and attractive banding patterns.

Gneiss is one of the most common metamorphic rocks in the Earth's crust. Some of the oldest known rocks on Earth are the Acasta Gneiss in Canada, dated to approximately 4.03 billion years ago.

Identify in the field by looking for distinct 'zebra-like' stripes of mineral segregation. Found worldwide in ancient cratons and metamorphic belts. Collectors look for unique swirling patterns or porphyroblasts (larger crystals like garnets) embedded in the bands.