metamorphic

Quartzite

Metamorphosed Quartz Sandstone (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Off-white, light gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Off-white, light gray, or tan
Luster: Vitreous to dull

Identified July 14, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing sand grains to recrystallize into a locked mosaic of quartz crystals. Can range from Proterozoic to more recent geological eras.

Uses & applications

Used in construction as crushed stone for road base or railway ballast, as dimension stone for counter tops and flooring, and as a source of silica for glass manufacturing.

Geological facts

Quartzite is so durable that when it breaks, it fractures through the individual sand grains rather than around them, unlike sandstone. It is often mistake for marble but is much harder and will not react with acid.

Field identification & locations

Identify by its extreme hardness (it will easily scratch glass) and its sugary, crystalline appearance on fresh breaks. Found globally in mountain belts and areas of uplifted metamorphic basement rock.