metamorphic
Quartzite
Quartzite (Primary mineral: Silicon Dioxide, SiO2)
Hardness: 7 on the Mohs scale; Color: typically white to gray, but iron oxides can cause pink, red, or tan tints; Luster: vitreous to waxy; Structure: non-foliated, granular crystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on the Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on the Mohs scale; Color: typically white to gray, but iron oxides can cause pink, red, or tan tints; Luster: vitreous to waxy; Structure: non-foliated, granular crystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, interlocking mosaic of crystals.
Uses & applications
Used heavily in construction as decorative stone, floor tiles, and countertop surfaces. In industry, it is used as a source of silica for glassmaking and as railroad ballast or road aggregate due to its extreme durability. Highly pure varieties are used to produce silicon metal.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is often confused with marble, but marble is soft and reacts with acid, whereas quartzite is chemically inert and highly resistant to weathering, often forming the caps of large mountain ranges.
Field identification & locations
Identify in the field by its sugary texture and inability to be scratched by a steel knife. It will break across the original sand grains rather than around them. Found globally in ancient mountain belts and shield areas like the Appalachians and the Canadian Shield.
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