Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to waxy; Crystal structure: Hexagonal (microcrystalline/interlocking); Cleavage: none; Specific gravity: approx. 2.65.

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. It can be found in mountain belts and areas of extreme tectonic activity.

Uses & Applications

Used in construction as crushed stone or road ballast, as a decorative stone in architecture (countertops and flooring), and historically for tool making due to its extreme hardness and durability.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the crests of ridges and hills, as it resists weathering more effectively than surrounding rocks. It cannot be scratched by a steel blade.

Field Identification & Locations

Identify in the field by its grainy, sandpaper-like texture (inherited from sandstone) but with a crystalline fracture that breaks across grains rather than around them. Found globally in ancient tectonic regions like the Appalachians or the Alps.

Identified on: 4/20/2026

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