metamorphic
Quartzite River Rock
Quartzite (SiO2 based metamorphic rock)
Hardness: 7 (Mohs), Color: Brownish-grey to tan, Luster: Dull to slightly vitreous when wet, Structure: Granular/Granoblastic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs), Color: Brownish-grey to tan, Luster: Dull to slightly vitreous when wet, Structure: Granular/Granoblastic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under heat and pressure. The specimen shows significant rounding and smoothing due to fluvial (river) or glacial abrasion over thousands of years.
Uses & applications
Used in landscaping, construction aggregate, road ballast, and as smooth decorative stones for gardens or aquariums.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as rounded cobbles in riverbeds for millions of years. It is much harder than the sandstone it originated from.
Field identification & locations
Identify in the field by its hardness (will scratch glass easily) and its rounded, water-worn shape. It lacks the visible grains feel of sandstone because the quartz grains have fused together.
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