metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (harder than glass). Color: brown, tan, or smoky grey (due to impurities). Luster: Vitreous to dull. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale (harder than glass)
- Color
- brown, tan, or smoky grey (due to impurities)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass). Color: brown, tan, or smoky grey (due to impurities). Luster: Vitreous to dull. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. The age can range from Precambrian to more recent geological eras depending on location.
Uses & applications
Extensively used in construction as crushed stone for road gravel and railroad ballast. Decorative uses include countertops, tiles, and landscaping. Occasionally used in jewelry or as a gemstone if the coloring is unique.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, frequently forming the peaks of mountain ranges. It is often confused with marble, but can be distinguished because quartzite will not fizz in acid and is much harder.
Field identification & locations
Identify in the field by its grainy, sandpaper-like surface that cannot be scratched by a steel knife. It breaks across grains rather than around them. Found globally in folded mountain belts and ancient crystalline shields.
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