metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-red (from iron oxide staining); Luster: Vitreous to dull; Crystal structure: Non-foliated, fused quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-red (from iron oxide staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-red (from iron oxide staining); Luster: Vitreous to dull; Crystal structure: Non-foliated, fused quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone under intense heat and pressure, typically during mountain-building events. These specimens likely date from the Proterozoic or Paleozoic eras.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and decorative landscaping. High-purity quartzite is used in glass and silicon production.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, forming prominent ridges and peaks in many mountain ranges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will scratch a pocket knife blade). Commonly found in the upper Midwest US (Sioux Quartzite) and Appalachian region. Collectors look for smooth river-tumbled pieces or richly colored blocks.
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