Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Grayish-brown with translucent patches; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, hard rock. It is found in mountain-building regions (orogens) dating from Precambrian to Cenozoic eras.

Uses & Applications

Used in construction as crushed stone or road ballast, as a dimension stone for flooring and wall coverings, and in the production of glass and silicon due to high silica content.

Geological Facts

Quartzite is so hard that it can scratch steel. Unlike sandstone, which breaks around individual sand grains, quartzite breaks across the grains due to the total recrystallization of the mineral.

Field Identification & Locations

Identify by its extreme hardness and sugary, crystalline texture on fresh breaks. It is commonly found in riverbeds as rounded cobbles or in massive mountain ridges. Not reactive to acid unlike similar-looking marble.

Identified on: 4/25/2026

Mode: Standard