metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often creates reddish, orange, or yellow hues like this specimen; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture despite its granular origins;…
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often creates reddish, orange, or yellow hues like this specimen; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture despite its granular origins; Specific gravity: approx. 2.6.
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to intense heat and pressure during regional metamorphism. The original sand grains recrystallize and fuse together, creating a much stronger and denser rock than its parent sandstone.
Uses & applications
Quartzite is widely used as crushed stone for road construction and railway ballast. Due to its resistance to chemical weathering and high hardness, it is also used for countertops, decorative building stone, and occasionally as a source of silica for glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms prominent ridges and resistant mountain tops in old mountain ranges. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than along the boundaries between them.
Field identification & locations
Identify in the field by its sugary, crystalline appearance on a fresh break and its inability to be scratched by a steel knife. This specimen is a 'river cobble,' meaning it has been naturally tumbled and smoothed by water transport in a stream or beach environment. Common in cratonic regions globally.
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