Quartzite

Hardness of 7 on the Mohs scale. Colors range from white and gray to pink, green, or yellow due to impurities. Vitreous to greasy luster with a non-foliated, granular crystal structure.

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic mountain-building events.

Used extensively in construction as crushed stone for road bases, dimension stone for architecture, and occasionally in the manufacture of silica brick and countertops.

Quartzite is extremely durable and resistant to chemical weathering, which is why parent sandstone ridges often weather into prominent mountain crests. Unlike sandstone, quartzite breaks across the quartz grains rather than around them.

Identify in the field by its hard, splintery fracture and inability to be scratched by a knife or glass. Commonly found in mountain belts worldwide, such as the Appalachian Mountains.