metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale (harder than glass). Color: Often white, gray, or brown but can be pink/red due to iron. Luster: Vitreous (glassy) to dull. Crystal structure: Granular, interlocking quartz crystals. It has no cleavage and a conchoidal fracture.
- Hardness
- 7 on Mohs scale (harder than glass)
- Color
- Often white, gray, or brown but can be pink/red due to iron
- Luster
- Vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass). Color: Often white, gray, or brown but can be pink/red due to iron. Luster: Vitreous (glassy) to dull. Crystal structure: Granular, interlocking quartz crystals. It has no cleavage and a conchoidal fracture.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together. These deposits can range from Proterozoic to more recent geological ages.
Uses & applications
Used widely in construction as crushed stone for road bases and railway ballast. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used in landscaping and as architectural dimension stone.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of ridges and mountains. Unlike sandstone, which breaks around grains, quartzite breaks through the grains.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch a steel knife) and its grainy, crystalline appearance. It is commonly found in mountain belts and areas of uplifted ancient basement rock. Collectors value it for its durability and occasional lapidary potential.
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