metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: tan, yellow, or light brown; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific gravity: approx 2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, yellow, or light brown
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, yellow, or light brown; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific gravity: approx 2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in orogenic belts. This specific specimen appears to be a water-worn river pebble or beach stone.
Uses & applications
Used in construction as crushed stone or decorative facing, in the glass industry if pure, and commonly collected as river stones for landscaping and home decor.
Geological facts
Quartzite is so durable that it can survive long periods of weathering and transport; it is often harder than the steel knife used to test it. It typically breaks through the quartz grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture. Common in ancient mountain ranges and glacial deposits.
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