metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish/tan; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none (conchoidal or irregular fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pinkish/tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish/tan; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none (conchoidal or irregular fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. It can be found in mountain belts and shield areas of various geological ages.
Uses & applications
Used primarily in construction for crushed stone, road ballast, and decorative building stone. In the glass industry as a source of silica. Also used for high-end countertops and as a collector's specimen when containing unique impurities.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and hills. It is often confused with marble, but can be distinguished because quartzite will scratch glass and does not fizz in acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to hydrochloric acid. It has a grainy, sugary appearance but feels smooth due to fusion. Commonly found in locations like the Appalachian Mountains or the Lake Superior region.
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