metamorphic
Quartzite River Cobble
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, tan, or iron-stained orange; Luster: Non-foliated, sugary to vitreous; Structure: Granoblastic macrocrystalline; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, tan, or iron-stained orange
- Luster
- Non-foliated, sugary to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: White, tan, or iron-stained orange; Luster: Non-foliated, sugary to vitreous; Structure: Granoblastic macrocrystalline; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone (protolith) under high pressure and temperature during mountain-building events. The 6-8 pound weight and rounded shape indicate extensive mechanical weathering and transport by river or glacial activity.
Uses & applications
Used primarily in construction (crushed stone), as ball mill media, or in landscaping. High-quality specimens are used for flintknapping or as decorative garden stones.
Geological facts
Quartzite is so hard that it will scratch glass and steel. This specimen was likely transported into the Kentucky/Ohio region (38.9°N) by glacial movement or ancient river systems during the Pleistocene epoch.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and rounded 'cobble' shape. Commonly found in riverbeds and glacial tills across the Ohio River Valley. In this region, they are often known as 'hardheads' by local farmers.
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