metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or tan with possible iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or tan with possible iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events (orogenic cycles). The process welds individual quartz grains together into a dense, crystalline matrix.
Uses & applications
Used in construction as crushed stone or decorative ballast, as dimension stone for counter tops and flooring, and historically for making stone tools due to its hardness and sharp fracture edges.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the peaks of mountain ranges because it resists weathering much better than the rocks surrounding it.
Field identification & locations
Identify by its ability to scratch glass easily and its lack of reaction to acid (unlike marble). It's commonly found in riverbeds or mountain outcrops. For collectors, look for high-purity or uniquely colored specimens.
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