Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.63 - 2.65.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure. This specific rounded specimen (cobble) suggests significant transport and erosion by water or glacial activity after its initial formation.

Uses & Applications

Used in construction as road ballast, railway ballast, and building stone. Crushed quartzite is used as a source of silica in glassmaking and metallurgy. Smooth specimens can be used in landscaping.

Geological Facts

Quartzite is so hard that it will scratch glass and steel. It is extremely resistant to chemical weathering, which is why it often remains as rounded cobbles in riverbeds long after other minerals have weathered away.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a steel blade) and its grainy, sandpaper-like texture that doesn't rub off. It lacks the distinct layers of sandstone because the sand grains have fused together. Common in mountainous regions and glacial deposits.

Identified on: 4/28/2026

Mode: Standard