metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, occasionally pink or reddish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, occasionally pink or reddish; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone or chert. Intense heat and pressure cause the quartz grains to recrystallize and fuse together, losing the original sedimentary texture. This process can occur across many geological ages from Precambrian to Mesozoic.
Uses & applications
Used in construction as crushed stone for road bases or railroad ballast, as dimension stone for flooring and wall coverings, and in the production of glass and industrial abrasives due to its high silica content.
Geological facts
Quartzite is so tough that it often forms the tops of ridges and mountains because it resists weathering better than surrounding rocks. It is harder than steel, and when it breaks, it fractures through the quartz grains rather than around them, unlike its precursor sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline appearance. It lacks the 'gritty' feel of sandstone because the pores are filled with silica. Common in mountainous regions like the Appalachians or the Alps.
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