metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs), Color: reddish-brown to grey, Luster: vitreous to dull, Structure: granular/crystalline, Cleavage: none, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs), Color: reddish-brown to grey, Luster: vitreous to dull, Structure: granular/crystalline, Cleavage: none, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone subjected to extreme heat and pressure, causing quartz grains to recrystallize and fuse.
Uses & applications
Used in construction as road ballast, railway ballast, and decorative stone. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, frequently forming the tops of ridges and mountains.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in mountainous regions or as rounded cobbles in riverbeds.
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