metamorphic
Yellow Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Yellow-orange to Tan; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-orange to Tan
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-orange to Tan; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, which causes the individual quartz grains to recrystallize and interlock. This specific specimen has been rounded by fluvial erosion in a river or stream bed.
Uses & applications
Used in construction as a decorative landscaping rock, as railroad ballast, and sometimes in the manufacturing of glass or ceramics due to high silica content.
Geological facts
Quartzite is so tough that it often outlasts the surrounding softer rocks during erosion, leading to the formation of ridges and resistant hills. Thousands of years ago, it was occasionally used as a substitute for flint to create stone tools.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its grainy, sandpaper-like texture even when polished. Commonly found in glaciated areas or riverbeds draining ancient mountain ranges like the Appalachians.
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