metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray with slight translucency; Luster: vitreous to grainy; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white to light gray with slight translucency
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray with slight translucency; Luster: vitreous to grainy; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together, creating a much harder rock. This occurs during mountain-building events in various geological ages.
Uses & applications
Used in construction for road ballast, roofing granules, and as a decorative stone in architecture. Due to its hardness, it is also used as a gemstone and for industrial abrasive products.
Geological facts
Quartzite is so hard that it can scratch steel and glass. It is often mistake for marble, but marble will fizz when exposed to acid while quartzite will not. Over time, quartzite can form prominent ridges in landscapes because it resists weathering better than surrounding rocks.
Field identification & locations
Identify by its sugary or crystalline texture that reflects light on fresh surfaces. It is extremely difficult to break and does not react with hydrochloric acid. Commonly found in folded mountain belts worldwide, such as the Appalachians or the Alps.
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