Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: Tan, yellowish, or white (typically colored by iron oxides). Luster: Vitreous to dull. Crystal structure: Non-foliated, interlocking quartz grains. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize quartz grains into a dense, hard rock. Typically lacks foliation due to the uniformity of minerals and pressure application.

Uses & Applications

Used widely in construction as crushed stone for road gravel and railway ballast. Polished specimens are used for decorative countertops, flooring, and wall cladding. Not typically used in fine jewelry but common in lapidary work.

Geological Facts

Quartzite is so hard and durable that it often survives intense surface weathering and forms the caps of ridges and mountains. It is significantly harder than the sandstone from which it originates.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that does not rub off. Common in many mountain ranges and riverbeds as rounded cobbles.

Identified on: 4/27/2026

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