Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: Honey-yellow to translucent white. Luster: Vitreous (glassy) to waxy. Crystal structure: Trigonal/Hexagonal. Cleavage: Indistinct. Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains and silica cement to fuse into a dense, crystalline rock. Common in mountain belts and Precambrian shield areas.

Uses & Applications

Used in construction as road ballast or aggregate, as a source for silica in glassmaking, and in decorative landscaping or jewelry (as tumbled stones).

Geological Facts

Quartzite is so hard that it will scratch glass and steel. It is often more resistant than the granite it may be found near, leading to the formation of ridges and peaks in mountainous terrain.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a knife) and its sugary/crystalline texture that breaks through grains rather than around them. Found globally in ancient metamorphic terrains.

Identified on: 4/13/2026

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