Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Yellow-brown to tan; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal system (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during orogenic (mountain-building) events. This specimen has been rounded by fluvial or marine water action.

Uses & Applications

Used in construction as crushed stone, road ballast, and decorative stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.

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, leading to the formation of ridges and resistant hilltops.

Field Identification & Locations

Identify by its hardness (cannot be scratched by a steel knife) and its grainy, sugary texture that resembles granulated sugar held together by glass. Common in riverbeds and glacial deposits.

Identified on: 5/5/2026

Mode: Standard