metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create reddish/brown tints; Luster: Vitreous to dull; Structure: Granoblastic (interlocking crystals); No cleavage; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create reddish/brown tints; Luster: Vitreous to dull; Structure: Granoblastic (interlocking crystals); No cleavage; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. These specimens appear to be river-worn pebbles, likely from the Holocene epoch but formed from ancient parent rock.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives. Smooth pebbles are used in landscaping and aquariums.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, leading to the formation of 'quartzite ridges' in mountain ranges. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary texture on fresh breaks. Found globally in ancient mountain belts and riverbeds. Look for the translucent look on edges.
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