Identify any rockfrom a photo.

Rounded dark river pebble

Likely fine-grained basalt or andesite; exact identification requires a fresh surface or tests

Weathered iron-rich basalt or volcanic breccia

Mafic volcanic rock, likely basalt; composition dominated by plagioclase and pyroxene with iron oxides

Weathered basalt or mafic volcanic rock

Basalt; typically plagioclase feldspar, clinopyroxene, and often olivine or iron oxides

Polished basalt with a quartz vein

Basalt, cut by milky quartz (SiO₂)

Milky quartz vein fragment

Quartz (silicon dioxide, SiO₂), massive/microcrystalline variety

Milky quartz

Quartz (silicon dioxide, SiO₂)

Rounded sedimentary pebble, likely mudstone or shale

Argillite/mudstone; predominantly compacted clay minerals with quartz and iron oxides

Fossilized coral or porous marine limestone

Likely fossil coral (Scleractinia), composed mainly of calcite/aragonite (CaCO₃)

Speckled granitic rock

Likely granite or granodiorite; quartz–feldspar–mica aggregate

Tumbled carnelian (likely chalcedony)

Carnelian, orange-red cryptocrystalline quartz (SiO₂), a variety of chalcedony

Quartz cluster, possibly druzy quartz on matrix

Quartz (SiO₂), likely microcrystalline to coarse crystalline; associated matrix uncertain

Quartz-rich rock with chlorite/epidote vein

Milky quartz with green chlorite or epidote; exact identification requires testing