metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: White to light grey with graininess; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: approx. 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White to light grey with graininess
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: White to light grey with graininess; Luster: Dull to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: approx. 2.65
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the sand grains to recrystallize and fuse together. This specimen has been further shaped by fluvial (river) or glacial erosion into a rounded pebble.
Uses & applications
Used as decorative gravel in landscaping, as a construction aggregate, and historically as a material for masonry. Fine varieties are used as ballast for railroads.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it formed, frequently appearing as resistant ridges or rounded river stones like this one. It is harder and more durable than the parent sandstone.
Field identification & locations
Identify in the field by its hardness (will scratch glass and steel) and its grainy, sugary texture. Unlike marble, it will not react with acid. Commonly found in riverbeds, glacial tills, and ancient mountain belts.
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