Mineral, Organic Gemstone

Chert (and Chalcedony)

Microcrystalline Quartz (SiO2)

Petrified Wood

Silicon Dioxide (SiO2) - Calcified / Silicified Wood

Diamond (appearing in jewelry)

Diamond (pure Carbon, C)

Petrified Wood

Silicified Wood (SiO2 - Quartz/Chalcedony replacement)

Chalcedony (Agatized Coral / Rough Chalcedony Node)

Silicon Dioxide (SiO2)

Petrified Wood

Silicified Wood (SiO2)

Sandstone

Arenite (primarily composed of SiO2)

Chert (often called Flint)

Chert (Microcrystalline Silicon Dioxide, SiO2)

Sandstone (with potential fossil inclusions)

Clastic sedimentary rock (primarily SiO2)

Citrine

Silicon Dioxide (SiO2) with iron impurities

Chert (Cherty Flint/Jasper variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Zebra Marble

Metamorphosed Alabaster/Limestone (CaCO3)

Picture Jasper

Silicon Dioxide (SiO2) - Opaque Chert/Quartzite variety

Agatized Fossil (Druzy Agate)

Silicon Dioxide (SiO2) replacing organic matter

Septarian Nodule

Septarian Concretion

Glauconitic Sandstone (Greensand)

Glauconitic Quartz Arenite (containing Glauconite, (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2)

Cubic Zirconia (CZ)

Zirconium dioxide (ZrO2)

Limestone (Concretionary or Tufa)

Calcium Carbonate (CaCO3)

Fossil Coral (Rugosa or Solitary Coral)

Rugosa (Order), often referred to as 'Horn Coral' (Lithostrotionella or Grewingkia)

Chert (Holey Stone)

Microcrystalline Quartz (SiO2)

Garden Quartz

Included Quartz (SiO2 with accessory minerals such as Chlorite, Hematite, or Feldspar)

Petrified Wood

Silicified Wood (SiO2)

Banded Chert

Cryptocrystalline Quartz (SiO2)

Sandstone (likely Fossilized Wood or Concrete Simulacrum)

Arenite / Silicified Wood / Anthropogenic Concrete

Moss Agate

Chalcedony (SiO2) with inclusions of manganese or iron oxides

Pyrite on Limestone

Iron Disulfide (FeS2) in Calcium Carbonate (CaCO3) matrix

Petrified Wood

Silicified Wood (SiO2)

Orthoceras Fossil in Limestone

Orthoceras (extinct genus of cephalopods) in Carboniferous or Devonian Limestone

Chert (Jasper/Limonitic Chert)

Microcrystalline Quartz (SiO2)

Petrified Wood

Silicified Wood (SiO2)

Ferruginous Chert

Microcrystalline Quartz (SiO2) with Iron Oxides

Fossilized Crinoid Stem Segment

Crinoid (Phylum Echinodermata, Class Crinoidea)

Moss Agate

Chalcedony (Silicon Dioxide with inclusions) - SiO2

Prehnite

Prehnite (Ca2Al2Si3O10(OH)2)

Green Moss Agate

Agate (Silicon Dioxide - SiO2 with inclusions of Manganese/Iron oxides)

Chert (specifically Flint or Jasper variant)

Microcrystalline Quartz (SiO2)

Septarian Nodule or Mud Crack Fossil

Septarian Nodule (Concretion)

Fossilized Shark Tooth

Scapanorhynchus (Sand Tiger Shark relative)

Petrified Wood

Silicified Wood (primarily SiO2)

Chert (often called Flint or Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Shale

Shale (comprised mostly of clay minerals and quartz)

Pyrite Geode (Sparkling Druzy)

Iron Sulfide (FeS2) in Sedimentary Nodule