Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often with tan or reddish streaks from iron oxidation; Luster: vitreous (glassy) to dull; Crystal structure: interlocking mosaic of quartz grains; Cleavage: none; Specific gravity: roughly 2.65.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz sand grains and silica cement to recrystallize into a dense, interlocking matrix. It is found in mountain belts and shield areas of almost all geological ages.

Uses & Applications

Used in construction as road ballast, roofing granules, and dimension stone for flooring or wall cladding. Pure varieties are used in the production of glass and silicon metal. It is also liked by landscape designers for its durability.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than the rocks surrounding it, forming prominent ridges and resistant hilltops. Unlike sandstone, which breaks around its grains, quartzite breaks across its grains due to its recrystallized structure.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance on fresh surfaces. It lacks the pores found in sandstones. It is common in ancient mountain ranges and glacial deposits.

Identified on: 4/21/2026

Mode: Standard