Sedimentary (Physico Chemical Precipitate)

Hematite

Iron(III) oxide (Fe2O3)

Hematite

Iron(III) oxide (Fe2O3)

Geode (unopened)

Calcedony-lined Geode (SiO2)

Agate (or Chalcedony)

Silicon Dioxide (SiO2)

Hematite

Iron(III) oxide (Fe2O3)

Banded Chert / Flint

Silicon dioxide (SiO2)

Raw honey calcite

Calcite (calcium carbonate, CaCO₃)

Iron-rich concretion or ironstone nodule

Likely goethite- and/or hematite-cemented ironstone; exact identification requires testing

Ironstone concretion (possibly limonite/goethite-bearing)

Limonite, a mixture of hydrated iron oxides, commonly including goethite (α-FeO(OH))

Sandstone (with Iron Oxide)

Quartz Arenite / Ferruginous Sandstone (SiO2 with Fe2O3)

Raw selenite (gypsum)

Gypsum, CaSO₄·2H₂O; translucent variety selenite

Selenite (gypsum)

Gypsum, CaSO₄·2H₂O; fibrous variety often called satin spar

Quartz Geode Cluster (Iron-stained Quartz)

Silicon Dioxide (SiO2)

Orange calcite

Calcite, calcium carbonate (CaCO₃)

Banded Sedimentary Rock

Sedimentary rock with Liesegang banding

Fossilized Crab Carapace (Concretion)

Decapoda (fossil), typically preserved in calcite or siderite concretion

Weathered iron-rich rock, possibly hematite-bearing basalt or ironstone

Uncertain; likely Fe-oxide-rich basalt/ironstone containing hematite (Fe₂O₃), magnetite (Fe₃O₄), and silicate minerals

Calcite crystal specimen

Calcite — calcium carbonate, CaCO₃

Weathered iron-rich rock, possibly limonite-bearing quartzite or altered basalt

Indeterminate; likely quartz (SiO₂) with iron oxides/hydroxides such as limonite/goethite

Banded Iron Formation

Banded Iron Formation (BIF)

Honey calcite crystal fragment

Calcite (CaCO₃), likely honey or amber calcite

Orange calcite

Calcite (calcium carbonate, CaCO₃)

Ironstone (iron-oxide-rich rock)

Ferruginous sandstone or ironstone; likely composed chiefly of goethite and/or limonite, with quartz and clay

Chert

Microcrystalline Quartz (SiO2)

Blue-green calcite

Calcite (CaCO₃), likely copper-bearing or otherwise inclusions-colored

Siltstone Pebble with Veining

Siltstone

Ironstone / iron-oxide-rich rock fragment

Likely limonite/goethite-rich ironstone; exact identification is not possible from the image alone

Chert (Flint Nodules)

Microcrystalline Quartz (SiO2)

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Yellow Jasper

Silicon Dioxide (SiO2) with Iron Oxide inclusions

Jasper

Microcrystalline Quartz (SiO2)

Amethyst Geode Segment

Silicon Dioxide (SiO2) with trace Iron impurities

Red Jasper

Silicon Dioxide (SiO2 with Hematite impurities)

Yellow Quartz

Silicon Dioxide (SiO2)

Yellow Calcite

Calcium Carbonate (CaCO3)

Green Calcite

Calcium Carbonate (CaCO3)

Hematite with Magnetite

Iron Oxide (Fe2O3)

Blue Chalcedony

Silicon Dioxide (SiO2)

Celestine (or Celestite) Geode

Strontium Sulfate (SrSO4)

Quartz Geode Fragment

Silicon Dioxide (SiO2)

Tumbled honey calcite

Calcite (calcium carbonate, CaCO₃)

Yellow Jasper

Silicon Dioxide (SiO2) with iron oxide inclusions