metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often creates yellow, reddish, or brownish hues (as seen in image); Luster: vitreous to dull; Crystal structure: trigonal (recrystallized grains); Cleavage: none (conchoidal fracture); 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 staining often creates yellow, reddish, or brownish hues (as seen in image); Luster: vitreous to dull; Crystal structure: trigonal (recrystallized grains); 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. These rocks can date back to any geological era from the Precambrian to the Cenozoic, depending on the mountain-building event.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for walls and floors. It is also used in the manufacturing of glass and ceramics due to its high silica content. Smoother river-worn specimens are popular in landscaping.
Geological facts
Quartzite is so durable that it often outlasts the surrounding rock, forming resistant ridges or hills. It is often confused with marble, but can be distinguished because quartzite is much harder and will not fizz when exposed to dilute hydrochloric acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its tendency to break through the sand grains rather than around them, unlike sandstone. Common in mountainous regions with a history of tectonic activity. Look for the 'sugary' texture of the recrystallized minerals.
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