Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow/brown (due to iron oxides); Luster: vitreous or dull; Structure: granoblastic, non-foliated; Cleavage: none, breaks with a conchoidal or splintery fracture.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, forming a dense, durable rock. Its age can range from Precambrian to relatively recent mountain-building eras.

Uses & Applications

Used in construction for road ballast, roofing tiles, and flooring. Due to its hardness and durability, it is also used for countertops, decorative stones, and as a raw material for silica in glass manufacturing.

Geological Facts

Quartzite is so hard and dense that when struck with a hammer, it typically breaks through the quartz grains rather than along the grain boundaries as sandstone does. It is one of the most chemically resistant rocks on Earth's surface.

Field Identification & Locations

Identify in the field by its hardness (it easily scratches glass) and its sugary, crystalline appearance on fresh surfaces. It is commonly found in fold mountain belts globally. To distinguish from sandstone, look for a fracture that goes through the grains rather than around them.

Identified on: 5/19/2026

Mode: Standard