metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, tinted yellow by iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal) but appears as interlocking grains; Cleavage: none; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan, tinted yellow by iron oxides
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, tinted yellow by iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal) but appears as interlocking grains; Cleavage: none; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone subjected to high heat and pressure. This recrystallizes the quartz grains into a hard, interlocking network. Geological age varies from Precambrian to more recent tectonic periods.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was part of, forming prominent ridges and peaks because it resists weathering better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and a sugary or grainy appearance that looks like sand but does not rub off. Common in mountainous regions like the Appalachians or the Alps.
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