Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: Tan, beige, or white with a slightly sugary appearance. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None; breaks with a conchoidal or irregular fracture. Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into an interlocking mosaic of crystals.

Uses & Applications

Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.

Geological Facts

Quartzite is so hard that it can scratch steel and glass easily. It is often more resistant to weathering than the surrounding rock types, which is why it frequently forms the peaks of mountain ranges.

Field Identification & Locations

Identify by its hardness (cannot be scratched by a knife) and its grainy, sugary texture. It is common in ancient mountain belts and shield areas worldwide, such as the Appalachian Mountains or the Scottish Highlands.

Identified on: 5/5/2026

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