metamorphic
River Rock (Quartzite)
Quartzite
Hardness: 7 on Mohs scale; Color: light gray to off-white; Luster: vitreous to waxy; Structure: non-foliated granoblastic; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- light gray to off-white
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: light gray to off-white; Luster: vitreous to waxy; Structure: non-foliated granoblastic; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, usually at convergent plate boundaries. The specimen shown is water-worn and smoothed by alluvial erosion.
Uses & applications
Primarily used in construction (road ballast, crushed stone), landscaping, and occasionally as an abrasive or in glass-making if high purity quartz is present.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming ridges and resistant peaks in mountain ranges.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sugary texture under magnification. Common in riverbeds and glacial deposits worldwide.
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