metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan (sometimes pinkish from iron oxide); Luster: vitreous (glassy); Crystal structure: trigonal (hexagonal system); Cleavage: none, typically fractures conchoidally; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or tan (sometimes pinkish from iron oxide)
- Luster
- vitreous (glassy)
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or tan (sometimes pinkish from iron oxide); Luster: vitreous (glassy); Crystal structure: trigonal (hexagonal system); Cleavage: none, typically fractures conchoidally; Specific gravity: approx 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together into a dense, hard rock. This specimen appears as an eroded river cobble found within sedimentary conglomerate or concrete matrix.
Uses & applications
Used widely in construction as crushed stone for road gravel and railway ballast. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. It is also used as decorative stone and in landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, standing out as ridges or peaks. 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 extreme hardness (it will easily scratch glass or steel) and sugary or grainy texture. It is commonly found in mountainous regions or as rounded pebbles in glacial drift and riverbeds worldwide.
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