igneous
River Cobble (Diorite or Meta-volcanic with Quartz Veining)
Diorite (with SiO2 quartz veins)
Hardness: 6-7 Mohs; Color: Mottled grey, green-black, and tan with yellowish-white veins; Luster: Dull to waxy; Texture: Phaneritic (medium-grained) to porphyritic; Cleavage: None visible in hand specimen.
- Hardness
- 6-7 Mohs
- Luster
- Dull to waxy
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled grey, green-black, and tan with yellowish-white veins; Luster: Dull to waxy; Texture: Phaneritic (medium-grained) to porphyritic; Cleavage: None visible in hand specimen.
Formation & geological history
Formed through the cooling of silica-intermediate magma beneath the Earth's surface. The specimen has been subsequently weathered and rounded by fluvial (river) action and shows secondary quartz or epidote mineralization in fractures.
Uses & applications
Primarily used as decorative stone in landscaping, crushed stone for construction aggregate, or as a tool for river-stone massage.
Geological facts
The rounded shape indicates this rock has traveled many miles down a riverbed, wearing away its sharp edges. The veins represent fractures that were later filled by hydrothermal fluids enriched in minerals.
Field identification & locations
Identify in the field by its speckled 'salt and pepper' appearance and rounded, water-worn surface. Commonly found in riverbeds, glacial tills, and coastal areas.
