metamorphic
River Cobble (Quartzite/Granite mix)
Quartzite-rich river stone
Hardness: 6-7 (Mohs scale); Color: Mottled tan, gray, and pink; Luster: Dull to waxy when wet; Structure: Granular/Massive; Cleavage: None; SG: 2.6-2.7
- Hardness
- 6-7 (Mohs scale)
- Color
- Mottled tan, gray, and pink
- Luster
- Dull to waxy when wet
Identified More metamorphic →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Mottled tan, gray, and pink; Luster: Dull to waxy when wet; Structure: Granular/Massive; Cleavage: None; SG: 2.6-2.7
Formation & geological history
Formed through the metamorphic recrystallization of quartz-rich sandstone or the cooling of felsic magma (granite), subsequently rounded by fluvial erosion in a river or glacial environment over thousands of years.
Uses & applications
Commonly used in landscaping, as aggregate in construction, or for decorative garden paths. Smooth specimens are popular for rock painting or as 'worry stones'.
Geological facts
These smooth, rounded shapes are the result of 'abrasion'—a process where rocks hit each other in moving water, wearing down sharp edges. This specific stone appears to be a conglomerate of various mineral grains including quartz and feldspar.
Field identification & locations
Identified by its rounded, water-worn exterior and lack of sharp edges. To identify in the field, look for smooth textures in stream beds, beaches, or glacial till deposits. They are ubiquitous in temperate fluvial systems.
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