metamorphic
Quartzite (Iron-stained)
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (scratches glass); Color: Buff, tan, or yellowish-brown due to iron oxide staining; Luster: Vitreous to greasy; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None (conchoidal fracture); Specific gravity: 2.63–2.65
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- Buff, tan, or yellowish-brown due to iron oxide staining
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale (scratches glass); Color: Buff, tan, or yellowish-brown due to iron oxide staining; Luster: Vitreous to greasy; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None (conchoidal fracture); Specific gravity: 2.63–2.65
Formation & geological history
Formed through the metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. These rocks can range from Precambrian to Cenozoic in age depending on regional tectonic history.
Uses & applications
Used extensively in construction as road ballast, railway track bedding, and crushed stone for concrete. Higher quality slabs are used for countertops, flooring, and decorative building facades.
Geological facts
Quartzite is so tough that it often outlasts other rocks during erosion, forming the resistant caps of many ridges and mountains. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness and 'sugary' texture on fresh breaks. It is commonly found in mountainous regions or glacial till. Collectors value large, well-rounded river cobbles or specimens with unique mineral inclusions.
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