Quartzite Cobble

Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: dull to vitreous, Crystal structure: non-foliated granoblastic, Specific gravity: 2.6-2.7

Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during regional metamorphism. This specific specimen has been rounded into a 'cobble' by water erosion in a river or beach environment.

Commonly used in construction as crushed stone or road ballast, as abrasive material, and as decorative landscaping stones. Higher purity quartzite is used to produce glass.

Quartzite is so durable that it can survive long periods of weathering and transport in high-energy river systems that would destroy most other rocks. It is harder than steel and will scratch glass.

Identify in the field by its extreme hardness, sandy texture on a micro-scale, and lack of reaction to acid. Often found in riverbeds, glacial deposits, or antigua beaches.