Rock Identifier
Sandstone or Quartzite with algae (Unknown specific, largely SiO2 with biological growth) — sedimentary or metamorphic
sedimentary or metamorphic

Sandstone or Quartzite with algae

Unknown specific, largely SiO2 with biological growth

AI-generated identification · may be incorrect

Hardness varies (6-7 for quartz-rich rocks). Tan, beige, grey color with bright green staining on the surface. Dull to earthy luster. Granular texture.

Identified More sedimentary or metamorphic →
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Physical properties

Hardness varies (6-7 for quartz-rich rocks). Tan, beige, grey color with bright green staining on the surface. Dull to earthy luster. Granular texture.

Formation & geological history

Formed from compressed sand (sandstone) or heated/pressurized sandstone (quartzite). The green coloration is likely from recent biological growth (algae or moss) due to being in a damp environment.

Uses & applications

Common rock type used in construction and landscaping, but this specific piece is likely just a found stone collected for its shape or color.

Geological facts

The bright green color is almost certainly biological, not a mineral stain like malachite or epidote, given the texture and context of beach/river rocks.

Field identification & locations

Identified by its granular texture and the superficial nature of the green coloration. Common in riverbeds, beaches, and damp soil.

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Other sedimentary or metamorphic specimens

Natural freshwater pearls (Pearl (nacreous calcium carbonate; chiefly aragonite, CaCO₃)) — gemstone

Natural freshwater pearls

Pearl (nacreous calcium carbonate; chiefly aragonite, CaCO₃)

gemstone
Dark gray rounded river pebble (Likely basalt or fine-grained volcanic rock; exact identification requires testing) — igneous

Dark gray rounded river pebble

Likely basalt or fine-grained volcanic rock; exact identification requires testing

igneous
Weathered dark stone, possibly basalt (Basalt; commonly plagioclase feldspar, pyroxene, and minor olivine) — igneous

Weathered dark stone, possibly basalt

Basalt; commonly plagioclase feldspar, pyroxene, and minor olivine

igneous
Painted River Rock (Artificially Coated Sedimentary Rock) — sedimentary

Painted River Rock

Artificially Coated Sedimentary Rock

sedimentary
Rounded gray river cobble (Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests) — sedimentary

Rounded gray river cobble

Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests

sedimentary
Mixed collection of common river stones (Varied lithologies, visibly including quartz-rich rock, dark mafic rock, sandstone, and purple quartz-bearing material) — igneous, sedimentary, metamorphic

Mixed collection of common river stones

Varied lithologies, visibly including quartz-rich rock, dark mafic rock, sandstone, and purple quartz-bearing material

igneous, sedimentary, metamorphic