metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or dirty white (stained by iron oxides); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or dirty white (stained by iron oxides)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or dirty white (stained by iron oxides); Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, usually at convergent plate boundaries. This specific specimen appears to be a river-worn cobble, smoothed by water transport long after its original formation.
Uses & applications
Used as crushed stone in road construction, as railway ballast, and occasionally for decorative landscaping or as industrial silica source.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them. It is one of the most resistant rocks to chemical and physical weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary texture on a fresh break. Commonly found in mountain belts or as rounded river rocks.
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