Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: Tan, beige, or white (often stained with iron oxides). Luster: Vitreous to dull. Crystal structure: Hexagonal (though usually appears as a dense interlocking mass of crystals). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the original quartz grains recrystallize and fuse together. These rocks can be of nearly any geological age but are common in ancient mountain belts.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and decorative landscaping. High-purity quartzite is used to produce glass and silicon metal. It is also used as dimension stone in architecture (slabs and tiles).

Geological Facts

Quartzite is one of the hardest and most chemically resistant rocks on Earth's surface. On mountain ridges, it often remains as the 'cap' because it erodes much more slowly than the surrounding rock types.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often feels 'gritty' like sandstone but breaks across the grain rather than around it. Found globally, especially in old metamorphic terrains.

Identified on: 4/15/2026

Mode: Standard