metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Gray, brown, or tan with possible reddish staining from iron oxides; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, brown, or tan with possible reddish staining from iron oxides; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. This specimen shows signs of alluvial wear, suggesting it was once tumbled in a river or stream. Geologic age can range from Precambrian to Cenozoic depending on the deposit.
Uses & applications
Commonly used in construction as crushed stone for road beds, railway ballast, and as a decorative stone in landscaping. Its high hardness makes it useful as a source of silica in glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the peaks of mountain ranges because it resists weathering better than surrounding rocks. It is often mistake for marble, but can be distinguished because quartzite will scratch glass and will not fizz in acid.
Field identification & locations
Identify in the field by its extreme hardness and grainy texture that sparkles when held up to the light (unlike chert which is smooth). This specimen is a typical 'river rock' found globally in glacial till or stream beds.
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