metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: tan, grey, pinkish; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan, grey, pinkish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, grey, pinkish; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. The individual quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used as a decorative stone, in construction as crushed stone or road ballast, as a high-silica raw material in glassmaking, and frequently as a lapidary material for tumbling.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and the way it breaks through quartz grains rather than around them (unlike sandstone). Commonly found in ancient mountain belts like the Appalachians or the Alps.
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