metamorphic
Quartzite
Quartzite (primarily SiO2 with iron oxide impurities)
Hardness: 7 on Mohs scale; Color: Rusty orange/brown surface due to limonite/hematite staining, white or grey interior; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Rusty orange/brown surface due to limonite/hematite staining, white or grey interior; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure from tectonic activity, the original quartz grains recrystallize and fuse together into a dense, hard mass. These specimens are often part of Proterozoic or Paleozoic formations.
Uses & applications
Used as crushed stone for road construction and railway ballast due to its extreme durability. Also used in glass making (if pure), as a decorative stone in landscaping, and occasionally as a building stone.
Geological facts
Quartzite is so hard that it will scratch window glass and steel. In the field, it is often distinguished from sandstone because it fractures through the grains rather than around them. The orange color seen here is a 'desert varnish' or iron oxide coating from weathering.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and sugary/granular texture on fresh breaks. Commonly found in folded mountain ranges. Collectors look for pieces with interesting iron staining patterns or those containing small crystals in vugs.
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