Gneiss

Hardness of 6-7 on Mohs scale, foliated texture showing distinct alternating light and dark bands (gneissic banding), vitreous to dull luster, specific gravity of 2.6-2.9.

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

Used primarily in construction as crushed stone for roadbeds, building foundations, and decorative facing stone.

Some of the oldest rocks on Earth, such as the Acasta Gneiss in Canada, have been dated to roughly 4 billion years old.

Easily identified in the field by its distinct compositional banding (alternating light-colored bands of quartz and feldspar and dark-colored bands of biotite or amphibole). Commonly found in ancient continental shields.