metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, purple, and brownish-red bands, Luster: vitreous to dull, Structure: Granoblastic, Cleavage: poor/none (fossilized conchoidal fracture visible in breakage)
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, purple, and brownish-red bands, Luster: vitreous to dull, Structure: Granoblastic, Cleavage: poor/none (fossilized conchoidal fracture visible in breakage)
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen shows water-worn rounding, suggesting original transport in a river or glacial environment.
Uses & applications
Used as decorative stone, construction aggregate, and highly valued as a durable landscaping material. High-purity quartzite is used in the manufacturing of glass and silicon.
Geological facts
Quartzite is so durable that it often survives multiple cycles of weathering and transport, outlasting the matrix of the original mountain ranges it formed in. It is harder than steel.
Field identification & locations
Identified by its extreme hardness (will scratch glass) and its granular, sugary texture on fresh breaks. Found commonly in riverbeds and glacial deposits across North America.
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