metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: tan, yellow-brown, or white (rusty staining due to iron oxides); Luster: vitreous to waxy; Structure: granular, non-foliated; Cleavage: none; 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: tan, yellow-brown, or white (rusty staining due to iron oxides); Luster: vitreous to waxy; Structure: granular, non-foliated; Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the individual quartz grains to recrystallize and fuse together into a dense, hard interlocking network. Usually found in mountainous or Precambrian shield regions.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and concrete aggregate. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon. It is also used in decorative landscaping and as dimension stone.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the peaks of hills and mountains. Unlike sandstone, which breaks around the grains, quartzite uniquely fractures across or through the quartz grains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It appears more translucent and crystalline than common sandstone. Found globally in ancient tectonic belts and riverbeds as cobbles.
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