Sedimentary Rock (Possibly A Conglomerate Or Coarse Grained Sandstone)

Red Sandstone

Clastic Terrigenous Sedimentary Rock (primarily SiO2 with Fe2O3 coating)

Siltstone / Shale River Rock

Siltstone (primarily SiO2 with Al2O3)

Biotite-rich gneiss (possibly mica schist)

Quartz–feldspar–biotite gneiss; mica-rich metamorphic rock

Sandstone (Garden Boulder)

Sandstone (SiO2 dominated)

Sandstone

Clastic sedimentary rock (primarily SiO2)

Sandstone

Clastic Sedimentary Rock (composed mostly of SiO2)

Weathered granite or granitic gneiss

Granite: quartz, feldspar, and mica; possibly gneiss if the dark minerals are banded

Metamorphic schist, possibly chlorite–biotite schist

Schist; composition likely quartz, feldspar, mica (biotite/muscovite), and chlorite

Graywacke

Graywacke (immature sandstone)

Gneiss (with Quartz-Feldspar vein)

Gneiss (high-grade metamorphic rock) containing Quartz (SiO2) and Feldspar (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)

Quartz Pebble

Silicon Dioxide (SiO2)

Breccia

Breccia (Clastic Sedimentary Rock)

Rounded yellow-brown cobble

Likely weathered sandstone or quartz-rich conglomeratic clast; exact identification requires a fresh surface and testing

Ferruginous Sandstone (with Pyrite/Gold associations)

Ferruginous Arenite (SiO2 + Fe2O3)

Gneiss (Gneissic Granite Pebble)

Metamorphic rock rich in Quartz, Feldspar, and Mica

Weathered granite or granodiorite boulders

Granite–granodiorite; chiefly quartz, feldspar, and dark mica/amphibole

Sandstone

Sandstone (clastic sedimentary rock)

Granite (weathered, possibly porphyritic)

Granite; primarily quartz (SiO₂), feldspars, and mica/amphibole

Agate (Puddingstone style)

Silicon Dioxide (SiO2) with impurities

Weathered iron-rich concretion or breccia

Goethite/hematite-bearing limonite concretion, possibly ferruginous sandstone

Sandstone

Sandstone (composed predominantly of Quartz, SiO2)

Quartzite (River Pebble)

Metamorphic rock consisting primarily of Quartz (SiO2)

Black Beach Pebble (Basalt / Slate Pebble)

Rounded Fine-Grained Clastic / Igneous Rock Pebble

Brecciated Jasper (or Polished Sedimentary Breccia)

Breccia / Microcrystalline Quartz (SiO2)

Red-brown quartzite or quartz-rich sandstone

Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with iron-oxide impurities

Small rounded pebble, likely weathered sandstone or iron-rich rock

Indeterminate; possibly quartz-rich sandstone (SiO₂) with iron-oxide staining

Likely gabbro or coarse-grained basalt

Gabbro (plagioclase + clinopyroxene ± olivine, Fe-Ti oxides)

Biotite-rich gneiss or schist

Mica gneiss/schist; primarily quartz, feldspar, biotite, and possibly amphibole

Gravel/Common Siltstone

Siltstone (fine-grained siliciclastic sedimentary rock)

Weathered sandstone or iron-rich sedimentary fragment

Quartz-rich sandstone, possibly ferruginous sandstone (SiO₂-dominant)

Weathered quartz-rich metamorphic rock, likely quartzite

Quartzite (mostly microcrystalline quartz, SiO₂), possibly altered sandstone

Sandstone

Arenite (SiO2 principal)

Granite

Granite, a coarse-grained felsic intrusive igneous rock composed mainly of quartz, feldspar, and mica

Rounded gray pebble, possibly limestone or quartzite

Uncertain; likely micritic limestone (calcite, CaCO₃) or fine-grained quartzite (quartz, SiO₂)

Rounded quartz-rich sandstone or quartzite cobble

Quartz-dominated siliciclastic rock; likely sandstone, possibly weakly metamorphosed quartzite

Sandstone

Arenite (SiO2 dominant)

Sandstone

Arenite

Rounded quartz-rich pebble, possibly chert or weathered sandstone

Indeterminate siliciclastic rock; likely microcrystalline quartz (SiO₂) or quartz-feldspar sandstone

Likely weathered granite or granitic rock

Granite; quartz + feldspar + mica, compositionally variable

Tumbled brown chert or flint pebble

Microcrystalline quartz (SiO₂), commonly called chert; exact identification is uncertain from the image

Sandstone (Iron-stained)

Clastic sedimentary rock (primarily SiO2 with Fe2O3 staining)

Sandstone

Arenite