Botryoidal Chalcedony
Silicon Dioxide (SiO2)
mineral
Category
Not A Geological Specimen
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Chevron Amethyst
Silicon dioxide, SiO2 (Quartz variety)
Mineral
Pyrite Geode
Iron Disulfide (FeS2)
mineral
Opal
Hydrated Amorphous Silica (SiO2·nH2O)
mineral
Jasper (Iron-stained Chert)
Silicon Dioxide (SiO2) with iron oxide inclusions
sedimentary
Orca Agate (Blue Chalcedony)
Silicon Dioxide (SiO2)
mineral
Green Aventurine
Aventurine Quartz (SiO2 with Fuchsite inclusions)
metamorphic
Blue Lace Agate
Chalcedony (Silicon Dioxide, SiO2)
mineral
Yellow Agate
Silicon Dioxide (SiO2)
mineral
Moss Agate
Silicon Dioxide with inclusions (SiO2 + Fe/Mg/Mn/Chlorite)
mineral
Quartz (Smoky Quartz variant)
Silicon Dioxide (SiO2)
mineral
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Gastropod Steinkern (Fossil Snail Internal Mold)
Class Gastropoda (Internal Mold)
sedimentary
Geode (Quartz chalcedony variety)
SiO2 (Silicon Dioxide)
sedimentary
Libyan Desert Glass
Impactite (High-silica tektite)
mineral
Breccia
Clastic Breccia
sedimentary
Quartz with Iron Oxide Inclusions
Silicon Dioxide (SiO2) with Hematite/Limonite
mineral
Quartz or possibly Jasper/Chert. Looks like a tumbled or water-worn stone.
SiO2 (Silicon Dioxide)
Mineral or Sedimentary (if chert)
Banded iron formation (BIF) / Chert
Banded Iron Formation (BIF), predominantly Microcrystalline Quartz (SiO2) and Iron Oxides (Fe2O3)
sedimentary
Granite
Granite (Felsic Plutonic Rock)
igneous
Ironstone Concretion (Moqui Marble)
Iron-oxide concretion (Fe2O3 / FeO(OH))
sedimentary
Petrified Wood
Silicified wood (Quartz/Chalcedony replacement of Cellulose)
fossil
Fossil Coral (Pleurodictyum)
Pleurodictyum sp. (Order Tabulata)
sedimentary
Amygdaloidal Rhyolite (often called Lake Superior Agate relative)
Rhyolite with Calcite/Quartz amygdules (SiO2 and secondary minerals)
igneous
Fossil Brachiopod Cast (Atrypa species)
Phylum Brachiopoda, Class Rhynchonellata, Order Atrypida
sedimentary
Carnelian Agate
Silicon Dioxide (SiO2) with iron oxide impurities
mineral
Granite
Granite (Felsic intrusive igneous rock)
igneous
Porphyritic Basalt (with Quartz or Calcite inclusion)
Porphyritic Basalt (Matrix: SiO2/MgO/FeO, Phenocryst: likely Quartz or Calcite)
igneous
Ironstone Concretion (Moqui Marble)
Hematite/Goethite Concretion (Fe2O3 / FeO(OH))
sedimentary
Shatter Cone (Impactite)
Shock-metamorphosed rock
metamorphic
Banded Iron Formation (Chert/Jasper)
Banded Iron Formation (BIF)
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2 - Silicon Dioxide)
sedimentary
Stromatolite
Biogenic Sedimentary Rock (composed predominantly of CaCO3)
sedimentary
Banded Iron Formation (BIF) / Iron Ore
Hematite-Magnetite BIF (Fe2O3 / Fe3O4 mixed with SiO2)
sedimentary
Quartz Geode
Silicon Dioxide (SiO2)
mineral
Garnet Schist
Almandine-Garnet Schist
metamorphic
Dyed Agate Slice
Silicon Dioxide (SiO2) - variety of Chalcedony
mineral
Quartz Vein in Host Rock
Silicon Dioxide (SiO2) within a metamorphic matrix
metamorphic
Sandstone
Arenite
sedimentary
Banded Quartz
Silicon Dioxide (SiO2)
mineral
Copper Ore with Malachite and Chrysocolla
Cu2CO3(OH)2 (Malachite) with Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (Chrysocolla)
mineral
Banded Calcite (Green Onyx)
Calcite (CaCO3)
sedimentary