metamorphic
Quartzite (River Pebble)
Metamorphic Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan with sugary white undertones; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline grains); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan with sugary white undertones
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan with sugary white undertones; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to heat, pressure, and chemical activity of metamorphism. This specific specimen has been further shaped by fluvial (river) erosion into a rounded cobble.
Uses & applications
Industrial uses include glassmaking and as a source of silica. In construction, it is used as crushed stone for road ballast or decorative landscaping stones.
Geological facts
Quartzite is so tough that it often survives where other rocks weather away; it is harder than a steel knife and will scratch glass easily. The yellow staining is likely from traces of iron oxide (limonite).
Field identification & locations
Identify in the field by its hardness (cannot be scratched by steel) and its crystalline, sugary appearance on a fresh break. Commonly found in riverbeds, glacial tills, and mountain ranges.
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