metamorphic
Quartzite (River Cobble)
Metamorphic Quartz-rich Rock
Hardness: 7 (Mohs scale), Color: Tan to reddish-brown (likely due to iron oxide staining), Luster: Dull/waxy when weathered, Crystal structure: Granoblastic (microcrystalline), Cleavage: None (conchoidal fracture)
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Tan to reddish-brown (likely due to iron oxide staining), Luster: Dull/waxy when weathered, Crystal structure: Granoblastic (microcrystalline), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under high heat and pressure. This specific specimen shows rounding and smoothing from transport in a river or stream environment.
Uses & applications
Used extensively in construction as crushed stone or ballast, and as a raw material for glass and ceramics if high purity; also used as landscaping rock.
Geological facts
Quartzite is one of the most durable and weather-resistant rocks on Earth. This piece likely contains iron impurities that give it its brownish hue, a process known as iron-oxide staining.
Field identification & locations
Identify in the field by its inability to be scratched by a steel nail, its granular texture (like sandpaper frozen in glass), and lack of fizzing when exposed to acid. Commonly found in riverbeds and mountainous regions.
More like this
