igneous and sedimentary

River Rock (Basalt/Greywacke pebbles)

Fluvial gravel primarily composed of Mafic Volcanic Rock (Basalt) or Lithic Sandstone (Greywacke)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: charcoal grey, olive green, dark brown; Luster: dull to waxy (when wet); Crystal structure: aphanitic or fine-grained; Cleavage: none; Specific gravity: 2.6 - 3.0

Hardness: 6-7 (Mohs scale)
Color: charcoal grey, olive green, dark brown
Luster: dull to waxy (when wet)

Identified March 29, 2026More igneous and sedimentary →

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At a glance

Common name: River Rock (Basalt/Greywacke pebbles)
Scientific name: Fluvial gravel primarily composed of Mafic Volcanic Rock (Basalt) or Lithic Sandstone (Greywacke)
Category: igneous and sedimentary
Identified: March 29, 2026
Method: Standard

AI Estimated Value

$0.05 - $0.50 per pound bulk market; $5.00 - $15.00 for small bags at retail; specimens with unique patterns can reach $10 - $20.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Hardness: 6-7 (Mohs scale); Color: charcoal grey, olive green, dark brown; Luster: dull to waxy (when wet); Crystal structure: aphanitic or fine-grained; Cleavage: none; Specific gravity: 2.6 - 3.0

Formation & geological history

Formed through volcanic cooling (basalt) or high-pressure sediment deposition (greywacke). They acquire their rounded, smooth shape through fluvial erosion (water transport in rivers) over thousands of years.

Uses & applications

Landscaping, drainage systems, construction aggregate, aquarium substrate, and decorative pathways.

Geological facts

River rocks are 'clastic' in origin, meaning they are broken pieces of older rocks. Most dark river stones like these are sourced from glacial deposits or active riverbeds in the Pacific Northwest or Appalachia.

Field identification & locations

Identify in the field by their smooth, rounded edges and lack of sharp points. Frequently found in riverbeds, lake shores, and glacial moraines. Collectors look for unique banding or 'lucky stones' with white quartz veins.