Sedimentary Rock (Specifically A Concretion Or Possibly A Geode)

Shale with Coprolite influence

Argillaceous sedimentary rock (Shale/Mudstone)

Limonite Geode / Ironstone Concretion

Hydrated iron oxide-hydroxide (FeO(OH)·n H2O)

White quartz geode

Quartz, silicon dioxide (SiO₂), likely a druzy quartz geode

Sandstone Concretion with Quartz Center

Sedimentary Clastic Rock (SiO2 matrix with Quartz core)

Septarian Nodule

Septarian Concretion (Complex of Calcite, Aragonite, and Limestone/Mudstone)

Ironstone Concretion (Coprolite-like)

Goethite/Hematite Siderite Spheroid (FeCO3 or FeO(OH))

Concretion

Sedimentary Concretion

Septarian Nodule (Dragon Stone)

Septarian concretion (Complex of Calcite, Aragonite, and Limestone)

Weathered chert or silicified limestone nodule

Microcrystalline quartz (SiO₂), possibly replacing limestone; exact identification requires testing

Quartz Geode

Silicon Dioxide (SiO2) in a concretion

Limonite Geode (Ironstone Concretion)

FeO(OH)·nH2O (Hydrated Iron Oxide)

Possible basalt or iron-rich concretion

Basaltic rock, likely composed mainly of plagioclase and pyroxene; exact identification requires testing

Sandstone Concretion

Sedimentary concretion

Druzy quartz geode

Microcrystalline quartz (SiO₂), commonly lining a volcanic geode cavity

Weathered iron-rich concretion or limonite/goethite nodule

Limonite (largely hydrated iron oxides; commonly goethite, FeO(OH), and hematite, Fe₂O₃)

Concretion

Various mineral compositions, typically carbonate or iron oxide cemented sediment

Ironstone Concretion / Goethite-Hematite Geode

Goethite / Hematite Concretion (Fe3O4 / FeO(OH) / Fe2O3)

Ironstone Concretion (Moqui Marble)

Iron-oxide Concretion (Hydrated ferric oxide, Fe2O3·nH2O)

Quartz Crystal

Silicon Dioxide (SiO2)

Concretion

Sedimentary Concretion (Ironstone / Calcite Concretion)

Agate Geode

Banded Chalcedony (Silicon Dioxide, SiO2) with Quartz crystals

Chalcedony Geode Fragment (Botryoidal)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Fossiliferous limestone, possibly containing a brachiopod or bivalve fossil

Calcite-rich limestone (CaCO₃), with an apparent shell impression or shell fragment

Limonite Geode / Ironstone Concretion

Hydrated Iron Oxide (FeO(OH)·nH2O)

Geode

Quartz nodule / Chalcedony-lined cavity

Jasper (or possibly Agate/Chalcedony) beads

SiO2 (Silicon Dioxide)

Quartz Druzy

Silicon Dioxide (SiO2)

Agate Geode (Unopened)

Cryptocrystalline Quartz (SiO2) with Chalcedony

Quartz (Druzy Quartz)

Silicon Dioxide (SiO2)

Weathered limestone or calcitic fossil/reef fragment

Calcite-rich limestone (CaCO₃), possibly fossiliferous limestone

Clear Quartz (Druzy)

Crystalline Silicon Dioxide (SiO2)

Quartz Geode

Silicon Dioxide (SiO2) within a sedimentary or igneous host

Amethyst

SiO2 (Silicon Dioxide with iron impurities)

Quartz Geode

Silicon Dioxide (SiO2)

Geode (Unopened)

Silica Concretion / Geode (Formula: SiO2 for quartz internal contents)

Chert (or possibly Flint)

SiO2 (Silicon Dioxide)

Quartz Geode

Silicon Dioxide (SiO2)

Amethyst (Rough)

Silicon Dioxide with iron impurities (SiO2)

Concretion

Sedimentary Concretion (e.g., Siderite or Ironstone)

Quartz Geode (partially formed/chalcedony with iron staining)

Quartz (SiO2) with Chalcedony (cryptocrystalline quartz) and likely Iron Oxides/Hydroxides

Quartz Geode

Silicon Dioxide (SiO2)

Quartz Geode

Silicon Dioxide (SiO2) within a geode