Gneiss

Mohs hardness of 6 to 7, banded appearance (gneissic banding) with alternating light and dark mineral layers, vitreous to dull luster, granular to crystalline structure, specific gravity around 2.6 to 2.9.

Formed by high-grade regional metamorphism, typically from preexisting igneous rocks (like granite) or sedimentary rocks (like shale or sandstone) subjected to intense heat and directed pressure deep within the Earth's crust.

Used primarily in the construction industry as crushed stone for road bases, building facades, landscaping, and occasionally as dimension stone for flooring and countertops.

Gneiss is one of the most common rocks in the Earth's continental crust and some of the oldest known rocks on Earth (dating back over 4 billion years, such as the Acasta Gneiss in Canada) are of this type.

Easily identified in the field by its distinct compositional banding (zebra-like stripes of light and dark minerals). Found globally in deeply eroded mountain belts and ancient shield areas.