Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or pink/red (due to iron oxide); Luster: vitreous to dull; Crystal structure: Hexagonal (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, causing the original quartz grains to recrystallize and fuse together. Often associated with regional oragenic (mountain-building) events.

Uses & Applications

Used in construction as crushed stone or road ballast, as a decorative building stone for countertops and flooring, and occasionally in glassmaking if the silica content is extremely high.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the tops of ridges and hills, as it erodes much slower than the surrounding rock. It is often confused with marble, but unlike marble, quartzite will not fizz in contact with acid.

Field Identification & Locations

Identify in the field by its extreme hardness (it will scratch glass) and its granular, sugary appearance on fresh surfaces. Often found in mountainous regions or as water-worn pebbles in riverbeds.

Identified on: 4/27/2026

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