metamorphic
Banded Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, and white banding; Luster: Vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, and white banding
- Luster
- Vitreous to waxy when polished
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, and white banding; Luster: Vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together, often preserving or creating banding based on original sedimentary layers or impurities.
Uses & applications
Used as a decorative stone, in jewelry (cabochons), as an abrasive, and in construction as crushed stone or dimension stone for flooring and walls.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along their boundaries. It is more resistant to weathering than the sandstone from which it originated, often forming prominent ridges or resistant outcrops.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture under a lens. Commonly found in metamorphic mountain belts like the Appalachians or the Alps. For collectors, look for distinct color banding caused by iron oxide or other impurities.
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