Not A Rock

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)

Biotite-bearing granite or granitic gneiss

Quartz–feldspar–biotite granite; possibly weakly foliated granitic gneiss

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

Basalt with Quartz/Quartzite Veins

Aphanitic Mafic Volcanic Rock with Siliceous Infillings

Quartz Vein in Siltstone

Silicon Dioxide (SiO2) within Sedimentary/Metamorphic Matrix

Botryoidal Chalcedony (Desert Rose / Agate)

Silicon Dioxide (SiO₂)

Granite

Granite (Felsic Plutonic Rock)

Basalt

Mafic extrusive igneous rock

Shale

Fissile Siliciclastic Sedimentary Rock

Mexican Cantera Opal

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

Milky quartz in dark host rock

Quartz (SiO₂), likely as a vein or vein fragment; host rock uncertain

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

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

Yellow Quartzite (River Pebble)

Quartzite (primarily Silicon Dioxide, SiO2)

Quartz Vein in Host Rock

Quartz (SiO2) in Mafic or Sedimentary Matrix

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)

Grey River Pebble (Greywacke / Basalt)

Stream-rounded silicate rock pebble

Rounded beach pebble

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

Basalt with Weathering Rind

Basalt (Mafic volcanic rock)

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

Shale

Shale (clastic sedimentary rock)

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

Chert (Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Biotite (Black Mica)

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

Quartz-rich chalcedony (likely silicified rock)

Microcrystalline quartz, SiO₂; possibly silicified limestone or jasper

Quartz geode

Crystalline quartz (SiO₂), lining a geode cavity

Weathered quartz pebble (tentative)

Quartz, SiO₂; possibly iron-stained quartz or quartz-rich rock

Quartz Geode

Crystalline Quartz (SiO2) within a sedimentary/igneous host

Quartz Geode

Silicon Dioxide (SiO2) in a sedimentary or volcanic host

Geode (Unopened)

Siliceous Geode (SiO2)

Tumbled dark volcanic rock, possibly basalt

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

Granite

Granite (Plutonic Igneous Rock)