metamorphic
Quartzite
Quartzite (composed primarily of Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-red to tan; Luster: Vitreous to dull; Crystal structure: Non-foliated granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-red to tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-red to tan; Luster: Vitreous to dull; Crystal structure: Non-foliated granoblastic; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed via the regional metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, interlocking matrix. This specimen shows signs of river-rounding (alluvial weathering).
Uses & applications
Used in construction for road ballast, flooring, and decorative stone. Historically used for making stone tools. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. It is often confused with marble, but quartzite will scratch glass and won't fizz in acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and sugary texture on fresh fractures. Commonly found in mountain belts where tectonic activity has occurred. Collectors look for unique colors or crystal inclusions.
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