metamorphic
Quartzite (Coldwater or Druzy Quartz over Quartzite)
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale; Color: Tan, beige, to off-white; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal) if macrocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, to off-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, to off-white; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal) if macrocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure Recrystallize the grains. Surface texture suggests later stage precipitation of quartz crystals or mineral etching.
Uses & applications
Commonly used in construction for crushed stone, decorative landscaping, and interior design (countertops). High-purity quartzite is used in glass making.
Geological facts
Quartzite is so hard that it will scratch glass and even surgical steel. It is more resistant to weathering than the original sandstone, often forming ridges or peaks in mountain ranges.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and lack of reaction to acid. The pitted, crystalline surface on this specimen suggests it may be a cast or have druzy quartz coatings.
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