metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but often reddish-brown due to iron oxide impurities; Luster: vitreous to dull; Crystal structure: hexagonal (as quartz grains); Cleavage: none; Specific gravity: approx 2.6
- 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 often reddish-brown due to iron oxide impurities; Luster: vitreous to dull; Crystal structure: hexagonal (as quartz grains); Cleavage: none; Specific gravity: approx 2.6
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. The original quartz grains recrystallize and fuse together, typically associated with mountain-building events (orogenies).
Uses & applications
Used in construction as crushed stone or road ballast, as a dimension stone for flooring or countertops, and as a raw material for glass and silicon ceramics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it erodes much more slowly than the surrounding rock types.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel) and its grainy, sugary texture that resembles sandstone but will break across the grains rather than around them. Common in eroded shields and mountain belts.
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