metamorphic
Quartzite Pebble
Metamorphosed Sandstone (mainly SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, and white; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6 to 2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, and white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, and white; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6 to 2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the quartz grains into a dense, interlocking mosaic of crystals. These pebbles are often rounded by water transport in rivers or beaches.
Uses & applications
Used in construction as crushed stone, in railway ballast, and as decorative landscaping stones. Tumbled or polished pebbles are used in crafts and jewelry.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, which is why it is frequently found as rounded river pebbles or cobbles. It is harder and more durable than the parent sandstone.
Field identification & locations
Identify by its extreme hardness (it will scratch glass easily) and its sugary, crystalline texture when broken. Commonly found in riverbeds, glacial deposits, and along coastlines near metamorphic terrains.
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