metamorphic
Quartzite (Iron-stained)
Quartzite (SiO2 with Fe2O3 staining)
Hardness: 7 on Mohs scale. Color: Tan, orange, or reddish-brown due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Hexagonal (trigonal) system, but usually appears as a dense crystalline mass. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, orange, or reddish-brown 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-brown due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Hexagonal (trigonal) system, but usually appears as a dense crystalline mass. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing the individual quartz grains to recrystallize and fuse into a solid rock. The yellowish-orange tint comes from groundwater leaching iron minerals into the rock.
Uses & applications
Used as crushed stone in construction, road ballast, and as a raw material for the manufacturing of glass and ceramics. Polished varieties are used for countertops and architectural stone.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them. It is one of the most durable rocks on the Earth's surface and often forms high ridges and hilltops because it resists erosion.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to acid. It typically looks recrystallized and sugary. Often found in glaciated regions or riverbeds as rounded cobbles.
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