Rock

Rounded quartz-rich pebble

Lithic pebble; likely quartz/quartzite with iron-oxide staining

River Stone (Sedimentary Sandstone/Quartzite)

Arenite/Quartzite transition specimen

Banded Sandstone Peabble

Arenite with iron oxide banding

Rounded quartz-rich pebble

Likely granitoid-derived quartz–feldspar rock; exact identification uncertain from image

Quartz Druzy (Geode Fragment)

Silicon Dioxide (SiO2)

Sandstone with Quarzite clasts

Arenite (SiO2 based)

Chert (Agatized/Chalcedony variety)

Microcrystalline Quartz (SiO2)

Chert (Jasper/Agate variety)

Microcrystalline Quartz (SiO2)

Tumbled dark volcanic rock, possibly basalt

Basalt; commonly composed of plagioclase feldspar, pyroxene, and minor olivine or magnetite

Basalt

Mafic extrusive igneous rock

Shale

Fissile Siliciclastic Sedimentary Rock

Basalt with Weathering Rind

Basalt (Mafic volcanic rock)

Mexican Cantera Opal

Amorphous hydrated silica (SiO2·nH2O) in Rhyolitic host rock

Polished river pebble

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

Sandstone with Quartz Vein

Arenite with Crystalline Silica (SiO2)

Copper-bearing porphyritic rock (likely bornite/chalcopyrite ore)

Altered porphyritic volcanic rock with copper sulfides, chiefly bornite (Cu₅FeS₄) and/or chalcopyrite (CuFeS₂)

Sandstone

Arenite (primarily SiO2)

Quartz with Chlorite inclusions

SiO2 with (Mg,Fe)3(Si,Al)4O10(OH)2⋅(Mg,Fe)3(OH)6

Green Jasper

Microcrystalline Quartz (SiO2)

Micaceous schist (likely biotite schist)

Biotite–quartz–feldspar schist; commonly containing muscovite and/or garnet

Fossil bivalve or brachiopod in sedimentary rock

Unidentified fossil shell impression; likely a ribbed bivalve or brachiopod preserved in shale/siltstone

Botryoidal Chalcedony (Desert Rose / Agate)

Silicon Dioxide (SiO₂)

Quartz Vein in Siltstone

Silicon Dioxide (SiO2) within Sedimentary/Metamorphic Matrix

Painted River Rock

Artificially Coated Sedimentary Rock

Yellow Quartzite (River Pebble)

Quartzite (primarily Silicon Dioxide, SiO2)

Quartz Vein in Host Rock

Quartz (SiO2) in Mafic or Sedimentary Matrix

Weathered granite or granitic pegmatite

Granite; primarily quartz (SiO₂), feldspar, and mica

Glacial erratic boulder, probably granite or granitic gneiss

Granite–gneiss; mainly quartz, feldspar, and mica

Mica-rich pegmatitic granite

Granitic pegmatite, chiefly quartz, feldspar, and muscovite/biotite mica

Red jasper in gray host rock (likely hematite-stained quartzite or rhyolite)

Jasper: microcrystalline quartz (SiO₂), with iron-oxide coloration; exact host uncertain from image

Basalt (Vesicular or Porphyritic River Pebble)

Mafic Volcanic Rock (Aphanitic to Porphyritic Basalt)

Greenschist (or Serpentinite) with Quartz-Feldspar Vein

Metabasalt / Greenschist Facies Rock

Quartz pebble

Silicon Dioxide (SiO2)

Quartz-rich chalcedony (likely silicified rock)

Microcrystalline quartz, SiO₂; possibly silicified limestone or jasper

Shale

Shale (clastic sedimentary rock)

Rounded beach pebble

Lithology indeterminate; likely fine-grained sandstone, mudstone, or weathered volcanic rock

Biotite (Black Mica)

Biotite - K(Mg,Fe)3AlSi3O10(F,OH)2

Basalt with Quartz Vein

Basaltic rock with hydrothermal SiO2 filling

Rounded gray river pebble, likely basalt or andesite

Fine-grained mafic volcanic rock; commonly basalt (plagioclase, pyroxene, and possible olivine)

Garnet Schist

Mica Schist with Almandine (Fe3Al2(SiO4)3)

Porphyritic Basalt

Porphyritic Basalt (with Plagioclase phenocrysts)

Porphyritic Basalt (with Pyrolusite or Iron-oxide staining)

Porphyritic Basalt (Mafic Extrusive)