metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale. Color: Off-white, yellowish, pinkish to light grey. Luster: Vitreous to dull/sugary texture. Crystal Structure: Trigonal (microcrystalline quartz network). Cleavage: None (conchoidal/irregular fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Off-white, yellowish, pinkish to light grey
- Luster
- Vitreous to dull/sugary texture
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Physical properties
Hardness: 7 on Mohs scale. Color: Off-white, yellowish, pinkish to light grey. Luster: Vitreous to dull/sugary texture. Crystal Structure: Trigonal (microcrystalline quartz network). Cleavage: None (conchoidal/irregular fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when pure quartz sandstone undergoes regional or contact metamorphism with high heat and pressure, causing quartz grains to recrystallize and interlock tightly. Common in Precambrian and Paleozoic metamorphic terrains.
Uses & applications
Used as decorative landscaping stone, aggregate for construction, railroad ballast, crushed stone for road bases, and historically as a tool stone due to its extreme hardness.
Geological facts
Quartzite is so hard and dense that when struck with a hammer, it fractures straight across the constituent quartz grains rather than along the boundaries between them (which distinguishes it from sandstone).
Field identification & locations
Identify by its interlocking sugary quartz grain surface, extreme resistance to scratching by steel, and rounded river-cobble shape. Commonly found in glaciated riverbeds, beaches, and mountain ranges worldwide.
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