metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, orange, yellow, or brown due to iron oxide impurities. It has a vitreous to greasy luster, a non-foliated massive crystal structure, lacks true cleavage and instead breaks with a conchoidal fracture, and has a specific gravity around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, orange, yellow, or brown due to iron oxide impurities. It has a vitreous to greasy luster, a non-foliated massive crystal structure, lacks true cleavage and instead breaks with a conchoidal fracture, and has a specific gravity around 2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during tectonic compression events in mountain-building processes (orogeny). Geological age varies widely depending on the formation location, ranging from Precambrian to Cenozoic eras.
Uses & applications
Used widely in construction as crushed stone for roadbeds, railway ballast, and as a decorative building stone or dimension stone for countertops and flooring.
Geological facts
Because quartz is extremely resistant to weathering, quartzite hills and ridges often stand out as prominent topographic features in landscapes where softer surrounding rocks have eroded away.
Field identification & locations
Can be identified in the field by its sugary texture on fractured surfaces and the fact that it cannot be scratched by a steel knife, unlike marble or limestone which it can superficially resemble. It breaks across the quartz grains rather than around them.
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