Rock Identifier
River Cobbles (Basalt, Quartzite, and Sandstone mix) (Fluvial detritus (primarily SiO2, Plagioclase, and Pyroxene mix)) — Mixed: Igneous and Sedimentary
Mixed: Igneous and Sedimentary

River Cobbles (Basalt, Quartzite, and Sandstone mix)

Fluvial detritus (primarily SiO2, Plagioclase, and Pyroxene mix)

Hardness: 6-7 (Mohs); Colors: gray, tan, dark blue-gray, off-white; Luster: dull to earthy; Structure: rounded/sub-rounded by water erosion; Cleavage: none (fractures irregularly); Specific Gravity: 2.5-3.0.

Hardness
6-7 (Mohs)
Luster
dull to earthy
Identified More mixed: igneous and sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Colors: gray, tan, dark blue-gray, off-white; Luster: dull to earthy; Structure: rounded/sub-rounded by water erosion; Cleavage: none (fractures irregularly); Specific Gravity: 2.5-3.0.

Formation & geological history

Formed through various processes (volcanic cooling for basalt, sedimentation for sandstone) and subsequently weathered and transported by high-energy river systems or glacial movement over thousands to millions of years.

Uses & applications

Landscaping, decorative garden 'cairns', construction aggregate, road base, and aquarium decor.

Geological facts

The smooth, rounded shape is a result of fluvial abrasion, where rocks tumble against each other in moving water. These specific stacked rocks are arranged in a 'cairn' style, historically used as trail markers or spiritual symbols.

Field identification & locations

Identify by a smooth, water-worn exterior and lack of sharp edges. Commonly found in riverbeds, glacial moraines, and coastal beaches. Collectors should look for unique banding or internal crystal textures revealed by polishing.

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Blue Calcite (commonly sold as Caribbean Calcite)

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River Pebbles and Quartz (Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)) — mixed

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Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

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Arkosic Sandstone (or Conglomeritic Sandstone fragment) (Arkose (rich in feldspar)) — sedimentary

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Arkose (rich in feldspar)

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General Gravel (River Rock/River Stones) (Mixed Lithic Sediments (Conglomerate Clasts)) — sedimentary

General Gravel (River Rock/River Stones)

Mixed Lithic Sediments (Conglomerate Clasts)

sedimentary
Dalmatian Stone (commonly called Dalmatian Jasper) (Peralkaline Rock (mixed Feldspar, Quartz, and Arfvedsonite)) — igneous

Dalmatian Stone (commonly called Dalmatian Jasper)

Peralkaline Rock (mixed Feldspar, Quartz, and Arfvedsonite)

igneous