metamorphic
Quartzite River Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Tan, beige, or off-white. Luster: Vitreous to dull when weathered. Structure: Non-foliated, granular crystalline structure with sugary texture. Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or off-white
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, beige, or off-white. Luster: Vitreous to dull when weathered. Structure: Non-foliated, granular crystalline structure with sugary texture. Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. This specific piece shows a rounded, water-worn shape, indicating it was transported over long periods by river or glacial action.
Uses & applications
Used widely in construction as crushed stone for road beds, railway ballast, and shoreline riprap. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative landscaping stone.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks. In thin sections, it can be seen that the recrystallization is so complete that the rock will break through the quartz grains rather than along the boundaries between them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its 'sugary' appearance when viewed closely. This specimen features 'chatter marks' or crescent-shaped impact scars on the surface, typical of high-energy transport in riverbeds.
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