metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale. Color: White, gray, or pinkish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 on the Mohs scale
- Color
- White, gray, or pinkish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: White, gray, or pinkish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating a very dense and durable rock. This process can occur over various geological ages, often in mountain-building zones.
Uses & applications
Used widely in construction as crushed stone for road gravel and railway ballast. Due to its hardness and resistance to weathering, it is used for floor tiles, wall coverings, and as a decorative stone in landscaping. Historically used for stone tools.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is much more resistant to chemical weathering than its parent sandstone. Some prehistoric human cultures used quartzite to make bifacial tools when 'better' materials like flint were unavailable.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel blade) and its granular, sugary appearance on a fresh break where crystals have fused. It's often found in folded mountain belts. Collectors should look for unique colors or bands created by mineral impurities.
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