metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale), Color: tan, brownish-red, gray or white, Luster: vitreous to dull, Structure: non-foliated granoblastic, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brownish-red, gray or white, Luster: vitreous to dull, Structure: non-foliated granoblastic, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic. Typically found in mountain belts (orogenic belts).
Uses & applications
Used in construction (railway ballast, road aggregate), interior design (countertops, flooring), and historically for stone tools.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming high ridges and mountains. It is differentiate from sandstone because quartzite breaks through the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness (scratches glass) and its sugary, crystalline surface. Common in metamorphic terrains and as water-worn pebbles in riverbeds.
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