metamorphic
Quartzite (River Pebble)
Metamorphic Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: tan to yellowish-brown; Luster: dull to waxy; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: approx. 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- tan to yellowish-brown
- Luster
- dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: tan to yellowish-brown; Luster: dull to waxy; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: approx. 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific rounded shape is the result of mechanical weathering and erosion in a fluvial (river) environment, likely over tens of thousands of years.
Uses & applications
Used primarily in construction as aggregate, landscaping, and as decorative river stones. High-purity quartzite can be used to produce silica for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the mountains it was formed in, becoming the rounded pebbles found in riverbeds long after the surrounding softer rocks have eroded away.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and lack of reaction to acid. Often found in riverbeds, glacial tills, and beaches worldwide. To collectors, these are often valued for lapidary work (tumbling).
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