metamorphic
River Quartzite (River Stone)
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or grey with translucent patches; Luster: Vitreous when wet or polished, dull when dry; Structure: Non-foliated granoblastic; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or grey with translucent patches
- Luster
- Vitreous when wet or polished, dull when dry
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or grey with translucent patches; Luster: Vitreous when wet or polished, dull when dry; Structure: Non-foliated granoblastic; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific specimen has been further shaped by fluvial (river) erosion, likely over thousands of years, resulting in its smooth, rounded 'cobble' shape.
Uses & applications
Used primarily as decorative landscaping stone, in construction aggregate, and occasionally for primitive tool making due to its extreme hardness and durability.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. In a river environment, these stones act as natural 'grinders' that erode softer rocks into sand while remaining largely intact.
Field identification & locations
Identify in the field by its smoothness, weight relative to size, and the lack of visible grains typical of sandstone. To confirm, try scratching it with a pocket knife; a steel blade generally will not leave a mark on true quartzite. Found globally in riverbeds and glacial tills.
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