Not A Rock

River Rock with Quartz Vein

Basalt or Andesite with Quartz Veining

Weathered stone pebble (exact rock type indeterminate)

Unidentified fine-grained rock; composition cannot be determined from the image

Weathered granite or granitic gneiss fragment

Granite; chiefly quartz (SiO₂), feldspar, and mica, with iron-oxide weathering

Granite, likely weathered biotite granite

Phaneritic intrusive igneous rock composed chiefly of quartz, feldspar, and biotite amphibole

Weathered volcanic rock, likely andesite or basaltic-andesite

Fine-grained plagioclase–pyroxene volcanic rock; possible altered andesite (exact identification requires testing)

Granite or granitic gneiss

Quartz–feldspar–mica granitoid; possibly foliated gneiss

Weathered granite or granitic gneiss

Quartz–feldspar–mica granitoid; possibly weakly gneissic

Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within metamorphic/igneous matrix

Unidentified dark gray rock fragment

Likely fine-grained basalt or andesite; exact identification requires testing

Rounded gray river pebble, likely fine-grained basalt or andesite

Basaltic-andesitic volcanic rock; commonly plagioclase feldspar, pyroxene, and minor iron oxides

Basalt

Aphanitic Mafic Volcanic Rock

Limestone

Calcium Carbonate (CaCO3)

Basalt

Extrusive Igneous Rock

Basalt Pebble

Extrusive Igneous Rock / Basalt

Serpentine

Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)3(Si, Al, Fe)2O5(OH)4

Granodiorite (Gneissic texture)

Granodiorite (containing Quartz SiO2, Plagioclase Feldspar, and Biotite)

Basalt (Vesicular)

Basalt (Extrusive Volcanic Rock)

Rock Specimen

Unclassified rock specimen

Amphibolite

Amphibolite, typically composed mainly of hornblende and plagioclase feldspar

Geode (Quartz / Chalcedony Geode)

SiO2 (Silicon Dioxide)

Vesicular volcanic rock, likely scoria

Scoria (vesicular basalt or andesite; exact composition cannot be confirmed from the image)

Rounded gray-brown pebble

Indeterminate; likely weathered quartz-rich sandstone or fine-grained volcanic rock

Quartz Geode

Silicon Dioxide (SiO2)

Coal (Bituminous / Anthracite)

Organic Sedimentary Rock (Carbonaceous Rock)

Coal

Coal (Sedimentary Rock / Organic Rock)

Painted River Pebble (likely Basalt or Greywacke)

Aphanitic Lithic Clast with Anthropogenic Pigment coating

Weathered greenish rock fragment

Tentatively altered basalt or serpentinite; exact identification requires testing

Quartzite Pebble

Quartzite (mostly SiO2)

Red Jasper (Beach Pebble)

SiO2 (Microcrystalline Quartz with Hematite inclusions)

Sandstone

Clastic sedimentary rock (primarily SiO2)

Polished dark-speckled igneous pebble, likely diorite or gabbro

Probable diorite (plagioclase feldspar and hornblende/biotite); exact identification is uncertain from the image

Sandstone Cobble with Iron Staining

Arenite with Limonite/Hematite staining

Red Sandstone

Arenite (Iron-rich)

Jasper and Quartz Breccia

Silicified Breccia (Quartz / Chalcedony / Hematite)

Gneiss (rounded cobble)

Quartz–feldspar–mica gneiss; exact mineral proportions cannot be determined from the image

Weathered granite or granitic gneiss boulder

Granite; predominantly quartz, feldspar, and mica (exact identification is uncertain from a photograph)

Granite-like rock

Felsic intrusive igneous rock, probably granitic or granodioritic

Rounded brown river pebble

Indeterminate lithic clast; possibly weathered sandstone or fine-grained volcanic rock

Petrified Wood

Silicified wood (primarily quartz, SiO2)

Fossilized Bark

Lepidodendron / Sigillaria fossil impression

River Pebble (likely Quartzite or Siltstone)

Sedimentary Clast (SiO2 based)

Quartz Geode (likely within Limestone or Dolomite matrix)

Quartz (SiO₂)