metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or reddish due to iron oxide; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or reddish due to iron oxide
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or reddish due to iron oxide; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking network of crystals.
Uses & applications
Extensively used in construction for road ballast, roofing granules, and as a decorative stone in architecture. Historically used for making tools due to its hardness and sharp edges when fractured.
Geological facts
Quartzite is so durable that it often forms the resistant ridges and peaks of mountain ranges. It is harder than steel and can easily scratch glass, which is a primary field test for identification.
Field identification & locations
Identify in the field by its granular, sugary texture and extreme hardness. It won't effervesce with acid (unlike marble). Common in mountain belts like the Appalachians or the Alps. For collectors, it is found globally where ancient sandstone beds have been folded.
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