metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to whitish with subtle pinkish/brownish tints, Luster: Vitreous to dull, Crystal structure: Hexagonal (microcrystalline/interlocking), Fracture: conchoidal or irregular, Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to whitish with subtle pinkish/brownish tints, Luster: Vitreous to dull, Crystal structure: Hexagonal (microcrystalline/interlocking), Fracture: conchoidal or irregular, Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into a dense, interlocking mosaic of crystals.
Uses & applications
Used in construction as crushed stone or road ballast, as dimension stone for flooring and countertops, in the production of glass and ceramics, and for manufacturing silica-based industrial products.
Geological facts
Quartzite is so tough that it often outlasts other surrounding rocks during erosion, often forming the caps of ridges and mountain peaks. It is frequently mistaken for marble but can be distinguished because quartzite will not react to acid and is much harder.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of visible individual sand grains (grains are fused). It is extremely common in ancient mountain belts like the Appalachians of North America or the Alps in Europe.
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