metamorphic
River Cobble (Quartzite or Chert)
Metamorphic Quarzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan, yellow, and grey banding, Luster: dull to waxy (slightly shiny when wet), structure: microcrystalline, specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, yellow, and grey banding, Luster: dull to waxy (slightly shiny when wet), structure: microcrystalline, specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The rounded shape indicates long-term transport and erosion in a high-energy river or stream environment.
Uses & applications
Primarily used in construction as aggregate, landscaping, or as decorative garden stones. If Jasper/Chert, can be used for tumbling.
Geological facts
Quartzite is one of the most physically durable and chemically resistant rocks found at the Earth's surface. This specimen shows a 'water-worn' patina known as a desert varnish or river polish.
Field identification & locations
Identify by its hardness (it will scratch glass) and lack of reaction to acid. Commonly found in riverbeds, glacial till, and coastal areas throughout North America and Europe.
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