Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, brown, white, or gray; Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed from the regional metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains and silica cement to recrystallize into a dense interlaced structure.

Uses & Applications

Used primarily as crushed stone for road construction and railway ballast. Also used as a decorative stone in landscaping and occasionally as dimension stone for stairs or flooring.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks during weathering, forming prominent ridges or hills known as 'quartzite monadnocks.' It is much harder and more durable than the sandstone it originates from.

Field Identification & Locations

Identify in the field by its hardness (it will easily scratch glass and stainless steel) and its granular, sugary appearance that breaks across grains rather than around them. Commonly found in mountainous regions or ancient shield areas.

Identified on: 4/17/2026

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