Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure. It is found in mountain-building belts worldwide and is typically hundreds of millions of years old.

Uses & Applications

Used as a decorative stone in architecture, as a source for silica in glass production, as railroad ballast, and occasionally as a gemstone in tumbled form.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock, forming prominent ridges and hills. It is often confused with marble, but quartzite will scratch glass while marble will not.

Field Identification & Locations

Identify in the field by its hardness (it can scratch glass) and its sugary, crystalline appearance. It is commonly found in metamorphic terrains such as the Appalachian Mountains or the Alps.

Identified on: 5/15/2026

Mode: Standard