metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here, but can be red or pink if containing iron; Luster: vitreous to matte; Crystal structure: hexagonal (polycrystalline mass); Cleavage: none, usually breaks across quartz grains; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to matte
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here, but can be red or pink if containing iron; Luster: vitreous to matte; Crystal structure: hexagonal (polycrystalline mass); Cleavage: none, usually breaks across quartz grains; Specific gravity: approx 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, creating a hard, dense rock. It can range from Precambrian to much younger geological ages.
Uses & applications
Used widely in road construction, as railroad ballast, and for architectural stone such as kitchen countertops or tiles. Low-purity quartzite is used in construction; high-purity varieties are used to produce silicon for electronics.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is frequently mistaken for sandstone, but when broken, sandstone breaks around its grains, while quartzite breaks through them. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness. Look for it in mountainous regions or along coastal outcrops where ancient sandstone has been buried. Collectors should look for unique colors or translucency near the edges.
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