Sedimentary (Chemically Precipitated)

Chert (Flint Nodules)

Cryptocrystalline Quartz (SiO2)

Veined Limestone

Calcite-veined Limestone (CaCO3)

Druzy Quartz on Limestone

Silicon Dioxide (SiO2) on Calcium Carbonate (CaCO3)

Banded Chert / Agate

Silicon Dioxide (SiO2)

Yellow calcite (honey calcite)

Calcite, calcium carbonate (CaCO₃)

Red Jasper with Quartz Veins

SiO2 (Silicon Dioxide with Iron Oxide inclusions)

Banded ironstone pebble

Banded iron formation (BIF), chiefly microcrystalline quartz/chert and iron oxides

Limestone

Calcium Carbonate (CaCO3)

Calcite-rich limestone

Limestone, predominantly calcite (CaCO₃), possibly recrystallized

Ferruginous Sandstone (Ironstone Nodules)

Ferruginous Sandstone with Limonite/Goethite coating (Fe2O3·H2O)

Orange Calcite

Calcium Carbonate (CaCO3)

Sandstone (Ferruginous)

Arenite (composed primarily of SiO2 with Fe2O3 cement)

Quartz (Rose Quartz or Jasper variety)

Silicon Dioxide (SiO2)

Dyed Agate Slice

Silicon Dioxide (SiO2) with artificial dyes

Chert / Flint

Microcrystalline Quartz (SiO2)

Sulfur-bearing Limestone (Solfatara Specimen)

Sulfur-rich Bio-limestone (Calcium Carbonate with Native Sulfur, S8)

Tumbled limestone or calcite-rich stone

Limestone, predominantly calcite (CaCO₃); exact identification is uncertain from the photograph

Ferruginous Sandstone

Arenite with Hematite/Goethite cement

Moqui Marble (Ironstone Concretion)

Goethite/Hematite Concretion (Fe2O3 / FeO(OH))

Ferruginous Sandstone

Arenite with Iron-oxide cement (composed of Quartz and Limonite/Hematite)

Sandstone (Ferruginous)

Arenite (iron-rich)

Weathered iron-rich concretion (probable limonite/goethite)

Limonite–goethite aggregate, approximately FeO(OH)·nH₂O

Chert

Microcrystalline Quartz (SiO2)

Weathered iron-rich concretion or ironstone nodule

Goethite–hematite limonite concretion (FeO(OH), Fe₂O₃, and hydrous iron oxides)

Flint/chert projectile point

Microcrystalline quartz (SiO₂), archaeologically worked into a bifacial point

Dendritic Siltstone (or Mudstone)

Siltstone with Manganese Oxide dendrites

Limestone

Calcium Carbonate (CaCO3)

Calcite-rich limestone fragment

Limestone, predominantly calcite (CaCO₃), possibly micritic or fossiliferous

Ferruginous Sandstone (Gritstone)

Arenite with Iron-Oxide Cement (SiO2 with Fe2O3 and FeO(OH))

Septarian Nodule Segment (Commonly known as Dragon Stone or Lightning Stone)

Septarian Nodule (CaCO3 / Hydrated Calcium Carbonate)

Septarian Nodule (Thunder Egg variant)

Septarian concretion (Calcite, Aragonite, and Limestone)

Chert

Microcrystalline Quartz (SiO2)

Psilomelane (Black Hematite/Manganese Ore)

Barium Manganese Oxide (Formula: BaMn9O18(OH)4)

Jasper

Microcrystalline Quartz (SiO2)

Travertine

Terrestrial Sedimentary Limestone (CaCO3)

Lake Superior Agate

Silicon Dioxide (SiO2) - variety: banded chalcedony quartzite

Banded Iron Formation

Banded Iron Formation (BIF)

Likely weathered limestone or calcite-rich stone

Limestone, primarily calcium carbonate (CaCO₃), possibly calcite

Chert (Vuggy or Weathered)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Dyed Agate Geode

Silicon Dioxide (SiO2) - Chalcedony variety

Banded limestone or marble

Calcite-rich carbonate rock; likely veined limestone, possibly low-grade marble (CaCO₃)