Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: White to light gray with yellowish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); 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 cause the quartz grains to recrystallize and fuse together, creating a look where grains are no longer distinct.

Uses & Applications

Used in construction as crushed stone or decorative landscaping. Higher purity specimens are used to produce silica sand for glassmaking or silicon metal production.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. It is harder than steel and will easily scratch a knife blade.

Field Identification & Locations

Identify in the field by its extreme hardness and the fact that it breaks across grain boundaries rather than around them. Commonly found in mountain belts and riverbeds as rounded 'river rocks' like this specimen.

Identified on: 4/22/2026

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