metamorphic
Quartzite
Metamorphic Quartz (SiO2)
Hardness: 7 (Mohs scale). Color: White, grey, or tan with frequent iron staining giving it a yellowish hue. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.63 - 2.65.
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale). Color: White, grey, or tan with frequent iron staining giving it a yellowish hue. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.63 - 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. Typically found in mountain belts (orogenic belts).
Uses & applications
Used in construction as crushed stone or decorative aggregate, in the glass industry as a source of silica, and as a durable material for countertops and flooring. Occasionally used in jewelry as river-tumbled stones.
Geological facts
Quartzite is so hard that it can scratch steel and glass easily. It is one of the most chemically and physically resistant rocks found on Earth's surface, often forming the caps of large mountain ridges because it resists erosion better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness and grainy but fused texture; unlike sandstone, it will break through the quartz grains rather than around them. Commonly found in riverbeds as smooth, rounded cobbles like the one pictured.
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