metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white to light gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. Under high heat and pressure, the quartz grains recrystallize and fuse together. It can be found in mountain ranges of almost any geological age.
Uses & applications
Used in construction (crushed stone), as a decorative stone in landscaping, in glass manufacturing if pure, and for making silica-based ceramics.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rock, forming prominent ridges and hills. It is often confused with marble but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular surface that looks like sand but cannot be rubbed off. Commonly found in folded mountain belts and ancient shield areas.
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