metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Tan, orange, or reddish due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Granoblastic (interlocking quartz grains). Cleavage: None. Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, orange, or reddish due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, orange, or reddish due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Granoblastic (interlocking quartz grains). Cleavage: None. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, creating a dense, non-foliated rock. This specimen appears water-worn, likely found in a riverbed or coastal environment.
Uses & applications
Used in construction as crushed stone or road ballast, as dimension stone for flooring and walls, and in glass manufacturing if pure enough. It is also a popular material for flintknapping tools and decorative landscaping.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion that destroys surrounding rock, forming prominent ridges and hills. It is often harder than the steel blade of a knife.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (it will easily scratch glass). Unlike sandstone, quartzite breaks across the individual grains rather than around them. Common in mountainous regions and glacial deposits.
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