metamorphic
Quartzite (Yellow/Orange variety)
Quartzite (composed primarily of Silica, SiO2)
Hardness: 7 on Mohs scale; Color: Honey-yellow, tan, or orange-brown due to iron oxide impurities; Luster: Vitreous to waxy; Structure: Granular/crystalline; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Honey-yellow, tan, or orange-brown due to iron oxide impurities; Luster: Vitreous to waxy; Structure: Granular/crystalline; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic plate boundaries cause the individual sand grains to recrystallize and fuse together into a dense, interlocking matrix. It can range in age from Precambrian to more recent geological eras.
Uses & applications
Commonly used in heavy construction as road ballast, crushed stone, or aggregate. Highly polished pieces are used for countertops, flooring, and decorative lapidary work (jewelry and carvings).
Geological facts
Quartzite is so tough that it often outlasts the surrounding softer rocks through erosion, forming prominent ridges or hilltops. Unlike sandstone, quartzite breaks through the sand grains rather than around them because of its dense crystalline structure.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular appearance on fresh surfaces. It is found globally in mountainous regions; notable deposits are in the Appalachians and Brazil. Collectors look for pieces with uniform color or unique translucency.
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