metamorphic
Riverstone (Water-worn Quartzite)
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Grayish-brown with possible tan/pink hues, Luster: Dull/Matte (earthy), Crystal structure: Granular crystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Grayish-brown with possible tan/pink hues, Luster: Dull/Matte (earthy), Crystal structure: Granular crystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under extreme heat and pressure. The rounded shape indicates extensive water erosion and transport in a fluvial (river) or glacial environment over thousands to millions of years.
Uses & applications
Commonly used in landscaping, as aggregate in construction, and in some cultures as 'worry stones' or for decorative garden features. High-purity quartzite is used in glass and silica production.
Geological facts
Quartzite is so tough that it often outlasts the surrounding softer rocks during erosion, ending up as rounded 'cobbles'. Some river stones found in ancient beds can date back hundreds of millions of years.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, rounded, ellipsoidal shape. Commonly found in riverbeds, beaches, and glacial till. Collectors look for unique colors or perfectly symmetrical shapes.
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