metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale; Color: typically white, gray, or brown but can be yellow/green due to impurities; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none; 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, gray, or brown but can be yellow/green due to impurities; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard mesh. Typically found in mountain-building zones or ancient continental shields.
Uses & applications
Used as a decorative stone in architecture (countertops, flooring), as railway ballast, in the manufacture of glass and ceramics, and as a source of silica in metallurgy.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the surrounding rocks, which results in quartzite forming prominent ridges and mountaintops in landscapes like the Appalachians.
Field identification & locations
Identify it by its extreme hardness (it will easily scratch glass and even steel) and its grainy, sandpaper-like surface that glitter in the sun. It won't effervesce with acid, distinguishing it from marble. Common in pebble form in riverbeds near mountainous regions.
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