metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown but can be tinged pink or red by iron oxide; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal/Hexagonal (parent mineral); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown but can be tinged pink or red by iron oxide; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal/Hexagonal (parent mineral); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure from tectonic compression or contact metamorphism. This process recrystallizes quartz grains into an interlocking network.
Uses & applications
Used widely in construction for railway ballast, decorative stone in countertops and walls, and historically as a hard material for making stone tools.
Geological facts
Quartzite is so durable that it often stays on mountain peaks after softer rocks have eroded away. It is often confused with marble, but can be distinguished by its hardness; quartzite will scratch glass, while marble will not.
Field identification & locations
Identify in the field by its grainy, sugary texture and high hardness (it will easily scratch a steel knife). Common in fold mountain belts globally. Tip for collectors: Look for pieces that show unique mineral inclusions or banding.
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