metamorphic
Quartzite (Tumbled Pebble)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale. Color: Tan, brownish, or cloudy white with iron inclusions. Luster: Vitreous to waxy. Structure: Granular/crystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brownish, or cloudy white with iron inclusions
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, brownish, or cloudy white with iron inclusions. Luster: Vitreous to waxy. Structure: Granular/crystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the sand grains to recrystallize and fuse together. These pebbles are often rounded by millennia of water transport in rivers or beaches.
Uses & applications
Used primarily as construction aggregate, ballast for railways, and decorative landscaping stone. Tumbled pieces are common in rock collections and used as ‘worry stones’.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify by its ability to scratch glass and its lack of reaction to acid. It is found globally in mountainous regions and riverbeds. Look for a sugary texture on broken surfaces and extreme hardness.
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