metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale. Color: white to light gray with brownish iron staining. Luster: dull to vitreous. Structure: granular and non-foliated. Cleavage: none, breaks with a conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Color
- white to light gray with brownish iron staining
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale. Color: white to light gray with brownish iron staining. Luster: dull to vitreous. Structure: granular and non-foliated. Cleavage: none, breaks with a conchoidal or irregular fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. Often found in Precambrian and Paleozoic mountain belts.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-quality specimens are used for countertops, floor tiles, and as a decorative stone in landscaping.
Geological facts
Quartzite is extremely resistant to chemical weathering. Because it is harder than glass or steel, it is one of the most durable materials on Earth, often forming the resistant ridges of mountain ranges.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its sugary, granular appearance when broken. Widely distributed globally; common in riverbeds, glacial tills, and mountain outcrops. A favorite among rockhounds for tumbling due to its durability.
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