metamorphic
Quartzite
Metamorphic Quartz Arenite
Hardness: 7 on the Mohs scale. Color ranges from white and grey to pink, yellow, or green depending on impurities. Luster is vitreous to greasy on fractured surfaces. Crystal structure is a dense interlocking network of quartz grains. Cleavage is absent (breaks across grains rather than along planes).…
- Hardness
- 7 on the Mohs scale
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Physical properties
Hardness: 7 on the Mohs scale. Color ranges from white and grey to pink, yellow, or green depending on impurities. Luster is vitreous to greasy on fractured surfaces. Crystal structure is a dense interlocking network of quartz grains. Cleavage is absent (breaks across grains rather than along planes). Specific gravity is approximately 2.65.
Formation & geological history
Formed when quartz-rich sandstone or chert is subjected to high heat and pressure, typically through tectonic compression during mountain-building events (regional metamorphism). Geological age varies widely depending on the formation site, ranging from Precambrian to Cenozoic.
Uses & applications
Used extensively in construction as crushed stone for roadbeds, railway ballast, and aggregate. Also utilized as a decorative dimension stone, in manufacturing refractory bricks, and increasingly as a durable countertop material in interior design.
Geological facts
Unlike its precursor sandstone, quartzite does not break around the sand grains; instead, the fractures break straight through the quartz grains due to the intense recrystallization under heat and pressure. It is extremely resistant to weathering and erosion, which is why ridges formed of quartzite often stand out as prominent hills or mountain crests.
Field identification & locations
To identify in the field, check for extreme hardness (scratches glass easily), an inability to effervesce with hydrochloric acid, and the signature sugary, sparkling appearance of broken quartz crystals on fresh fracture surfaces. Commonly found in mountain belts worldwide, such as the Appalachian Mountains in North America.
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