Not A Rock

Red granite or granitic gneiss cobble

Quartz–feldspar–mica rock; likely granite, possibly gneiss

Pink-and-black granite

Biotite-bearing granite, chiefly quartz, feldspar, and biotite mica

Weathered limestone

Calcite-rich limestone (CaCO₃), possibly fossiliferous or dolomitic

Orbicular granite (likely rapakivi-type granite)

Granite; chiefly quartz, alkali feldspar, plagioclase, and biotite/hornblende

Slickenside

Tectonic Fault Scarp Surface

Coarse-grained granite or granitic pegmatite fragment

Granite; primarily quartz, feldspar, and mica

Weathered limestone or dolostone

Calcite-rich limestone (CaCO₃), possibly dolomite-bearing

Pink Granite

Phaneritic Quartz-Feldspar Plutonic Rock

Shale

Shale (clastic sedimentary rock composed of silt and clay-sized particles)

Dalmatian Jasper / Dalmatian Stone

Peralkaline Rock (Silicon Dioxide with Amphibole inclusions)

Shale

Fissile mudstone (Shale)

Quartz Geode

Silicon dioxide (SiO2)

Basalt

Extrusive Igneous Rock

Ulexite

NaCaB5O6(OH)6·5H2O

Basalt

Aphanitic Mafic Igneous Rock

Vesicular Basalt (Lava Rock)

Basalt (Vesicular Variety)

Serpentine

Antigorite, Lizardite, or Chrysotile (Mg, Fe)3Si2O5(OH)4

Quartzite

Quartzite (primarily SiO2)

Sandstone (Ferruginous)

Arenite with Iron Oxide (Limonite/Hematite) coating

Quartz-veined metamorphic rock, likely quartzite or schist

Quartz-rich metamorphic rock with a milky-quartz vein; exact host rock is indeterminate from the photo

Alluvial stream gravel (mixed rock specimens)

Polymictic fluvial deposit; likely mixtures of quartzite, sandstone, shale, chert, basalt, and granite-derived minerals

Weathered quartz-rich rock, possibly granite or quartzite

Indeterminate; likely quartz–feldspar aggregate, possibly altered granite

Serpentine-rich metamorphic rock

Serpentinite, likely antigorite/lizardite with accessory magnetite or chromite

Granite Pebble

Intrusive Igneous Rock

Scoria

Scoria

Granite

Intrusive Igneous Rock

Carnelian agate

Cryptocrystalline quartz (SiO₂), iron-oxide-bearing chalcedony

Unidentified Rock

Unknown

Mica Schist

Mica Schist (primarily Muscovite or Biotite sheet silicates)

River Rocks (Black)

Various lithologies (e.g., basalt, chert, obsidian for black varieties), mechanically rounded clasts

Quartz with Host Rock

Silicon Dioxide (SiO2)

Vesicular Basalt with Epidote

Vesicular Basalt (Mg, Fe)2SiO4 with Epidote (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH))

Sandstone Concretion

Moqui Marble / Ironstone Concretion (Iron oxide-cemented sandstone)

Conglomerate (Quartz Pebble Conglomerate)

Quartz Pebble Conglomerate

Granite Pebble

Granite

Likely weathered granite or granitic gneiss

Granite: quartz + feldspar + mica; possibly gneiss if the faint texture reflects foliation

Granite with a polished dark-red granite cobble

Granite; predominantly quartz, feldspar, and mica

Weathered garnet-bearing gneiss

Quartz–feldspar–mica gneiss with almandine garnet, chiefly Fe₃Al₂(SiO₄)₃

Druzy Quartz on Matrix (likely Limestone or Sandstone)

Silicon Dioxide (SiO2) with various trace impurities

Quartz Druzy (on Matrix)

Silicon Dioxide (SiO2)

Weathered mafic rock, likely basalt

Basalt; primarily plagioclase feldspar, pyroxene, and minor olivine or iron oxides

Quartz Veined Basalt

Mafic Volcanic Rock with Microcrystalline Quartz (SiO2)