metamorphic
Quartzite
Metamorphic rock primarily composed of Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, but often pinkish-red or brown due to iron oxide staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with a conchoidal or irregular fracture); SG: 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 grey, but often pinkish-red or brown due to iron oxide staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with a conchoidal or irregular fracture); SG: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. Often found in orogenic belts and tectonic plate boundaries.
Uses & applications
Used as a decorative stone in architecture, road ballast, railroad track beds, and as a source of silica in glass manufacturing. Also high-value for countertop surfaces due to its durability.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during weathering, forming prominent ridges and peaks in mountainous terrain. It is much harder than sandstone and will scratch glass and steel.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks across the quartz grains rather than around them (unlike sandstone). Commonly found in the Appalachian Mountains and the Lake Superior region.
