Sedimentary (Chemically Precipitated)

Pyrite

Iron Sulfide (FeS2)

Green Calcite

Calcium Carbonate (CaCO3)

Orange Calcite

Calcium Carbonate (CaCO3)

Quartz on Limestone

Silicon Dioxide (SiO2) on Calcium Carbonate (CaCO3)

Yellow Calcite

Calcite (Calcium Carbonate, CaCO3)

Milky or Iron-Stained Quartz

Quartz (Silicon Dioxide, SiO2)

Orange Calcite

Calcium Carbonate (CaCO3)

Banded iron formation (specimen, possibly hematite–jasper)

Banded iron formation; chiefly hematite (Fe₂O₃), magnetite (Fe₃O₄), and silica (chert/quartz), with possible limonite/goethite staining

Banded Calcite Onyx (Cave Onyx / Mexican Onyx)

Calcite (CaCO3) / Travertine

Light-colored limestone pebble

Calcite-rich limestone (primarily CaCO₃)

Banded iron formation (ironstone)

BIF; alternating hematite/magnetite and chert (SiO₂) layers

Green Chert

Microcrystalline Quartz (SiO2)

Eroded Limestone with Iron Staining

Carbonate Rock (CaCO3)

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Likely calcite specimen

Calcite, calcium carbonate (CaCO₃)

Agate

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Limonite / Ironstone

Hydrated ferric oxide (FeO(OH)·nH2O)

Limonite (Iron Ore/Sandstone mixture)

Limonite (FeO(OH)·nH2O) often mixed with Goethite and sedimentary matrix

Banded Iron Formation (BIF) / Chert

Banded Iron Formation (SiO2 with Fe2O3 / Fe3O4)

Septarian Nodule

Septarian Concretion (Composition: Calcite, Aragonite, and Limestone/Clay)

Banded iron formation (banded ironstone)

BIF, chiefly hematite/magnetite and microcrystalline quartz (chert); locally limonite/goethite

Rounded limestone pebble

Limestone, predominantly calcite (CaCO₃)

Calcite-rich limestone

Limestone, predominantly calcium carbonate (CaCO₃), usually calcite

Chert with Quartz Vein

Microcrystalline Quartz (SiO2)

Banded Onyx (Green Onyx)

Banded Calcite or Travertine (CaCO3)

Limonite (Yellow Ochre)

Limonite (an amorphous mixture of hydrated iron oxides, primarily FeO(OH)·nH2O)

Red Jasper

Microcrystalline Quartz (SiO2)

Jasper

Microcrystalline Quartz (SiO2)

Limestone

Calcium carbonate (CaCO3) / Limestone

Ferruginous Sandstone (Ironstone)

Sedimentary rock with Limonite/Goethite cement

Quartz Druzy / Quartz Crystal Cluster

Silicon Dioxide (SiO2)

Flint (Chert)

Cryptocrystalline Silica (SiO2)

Limestone with Calcite Veining

Calcium Carbonate (CaCO3)

Calcite

Calcium Carbonate (CaCO3)

Aragonite (Onyx Marble)

Calcium Carbonate (CaCO3), Orthorhombic crystal system

Yellow Jasper

Silicon Dioxide with iron inclusions (Quartz variety)

Polished banded ironstone pebble

Banded iron formation (BIF), chiefly hematite/magnetite and quartz

Banded ironstone pebble

Banded iron formation (BIF), chiefly quartz/chert and iron oxides; possibly hematite–magnetite-rich jasper

Banded iron formation (iron-rich chert), possibly jasper

Banded iron formation; alternating microcrystalline quartz (SiO₂) and iron oxides/hydroxides (hematite, magnetite, goethite)

Banded iron formation fragment (iron-rich chert/jasper)

Banded iron formation; microcrystalline quartz (SiO₂) with hematite/magnetite and iron oxides

Banded iron formation (ironstone), likely hematite–magnetite jasper

Banded iron formation (BIF), chiefly Fe₂O₃ hematite, Fe₃O₄ magnetite, and SiO₂ quartz/chert

Coquina Limestone (Fossiliferous Limestone)

Calcareous bioclastic sedimentary rock (CaCO3)