metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here due to iron staining; Luster: vitreous to dull; Crystal Structure: non-foliated, interlocking quartz grains; Cleavage: none, breaks with a conchoidal or splintery fracture.
- 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, gray, or yellowish as seen here due to iron staining; Luster: vitreous to dull; Crystal Structure: non-foliated, interlocking quartz grains; Cleavage: none, breaks with a conchoidal or splintery fracture.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse into a dense, hard metamorphic rock. This specific specimen appears to be a river-worn cobble or pebble.
Uses & applications
Used widely in construction as crushed stone for roadbeds or railway ballast. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone in landscaping and architecture.
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion that destroys other rocks, which is why it is frequently found as rounded cobbles in riverbeds. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. In the field, look for a sugary or sparkly texture on fresh breaks where quartz grains reflect light. Common in mountain ranges and ancient shields worldwide.
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