metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or pale orange (iron-stained); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific Gravity: 2.6-2.7. It is very hard and will scratch glass easily.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or pale orange (iron-stained)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or pale orange (iron-stained); Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific Gravity: 2.6-2.7. It is very hard and will scratch glass easily.
Formation & geological history
Formed through the metamorphism of quartz sandstone. Intense heat and pressure caused the original quartz sand grains to recrystallize and fuse together, creating a tough, interlocking crystalline structure. These formations often span hundreds of millions of years from the Proterozoic to Paleozoic eras.
Uses & applications
Used as crushed stone in road construction, railway ballast, and as a decorative stone in architecture. Due to its durability, it is also used in manufacturing glass and ceramics when high purity is present, as well as for countertops and exterior cladding.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as resistant ridges or peaks. Unlike sandstone, which breaks between grains, quartzite breaks through the grains due to the complete recrystallization of the silica.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy but fused texture. It is found worldwide in mountainous regions or stable continental interiors. Collectors look for unique colorations caused by mineral impurities like iron or chromium.
