metamorphic
Quartzite Cobble
Quartzite
Hardness: 7 (Mohs scale), Color: tan to light grey, Luster: vitreous to dull, Crystal structure: granular/crystalline (microscopic), specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light grey, Luster: vitreous to dull, Crystal structure: granular/crystalline (microscopic), specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, often in orogenic (mountain-building) zones. This specimen appears weathered and rounded by water transport.
Uses & applications
Commercial use includes road ballast, railway ballast, and as a raw material for glass making. Small rounded specimens are often collected as river stones or used in landscaping.
Geological facts
Quartzite is so hard that it will scratch glass and even stainless steel. In the field, it can be distinguished from sandstone because it breaks across the quartz grains rather than around them.
Field identification & locations
Can be identified by its extreme hardness and sugary crystalline fracture surface visible at the chip. Commonly found in riverbeds, glacial tills, and mountainous regions worldwide.
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