Mineral, Specifically An Iron Ore

Blue Sapphire (in a faceted jewelry setting)

Corundum (Al2O3) with trace Iron and Titanium

Specular Hematite

Iron Oxide (Fe2O3)

Tourmalinated Quartz

Silicon Dioxide (SiO2) with inclusions of Schorl (NaFe2+3Al6Si6O18(BO3)3(OH)3OH)

Montana Moss Agate

Chalcedony (Silicon Dioxide, SiO2)

Pyrite or Chalcopyrite

Iron sulfide (FeS2) or Copper iron sulfide (CuFeS2)

Chalcopyrite in Quartz (Gossan/Iron Hat)

CuFeS2 (Chalcopyrite) with SiO2 (Quartz)

Small dark mineral/rock fragment

Indeterminate; possibly magnetite-bearing basalt or iron-rich slag

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Dendritic Agate

Silicon Dioxide (SiO2) with Manganese/Iron inclusions

Limonite

Hydrous Iron Oxide (often Goethite FeO(OH), Lepidocrocite γ-FeO(OH), and other amorphous iron oxyhydroxides)

Jasper

Silicon Dioxide (SiO2) with iron oxide impurities

Turquoise and Hematite

Turquoise (CuAl6(PO4)4(OH)8·4H2O) and Hematite (Fe2O3)

Moonstone (Green Moonstone / Garnierite)

Potassium Aluminum Silicate (KAlSi3O8) with inclusions of Garnierite

Yellow Ochre / Limonite

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

Orange Calcite

Calcium Carbonate (CaCO3)

Limonite (Ironstone Concretion)

Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)

Limonite (Ironstone)

Hydrated Iron Oxide (FeO(OH)·nH2O)

Blue Sapphire

Corundum (Al2O3 with trace Titanium/Iron)

Iron-rich laterite or weathered ironstone pebble

Goethite–hematite-rich ferruginous duricrust; commonly approximated as FeO(OH) and Fe₂O₃

Hematite Nodule

Hematite (Fe2O3)

Limonite (Ironstone)

Hydrous ferric oxides (FeO(OH)·nH2O)

Druzy Quartz on Sandstone

Silicon Dioxide (SiO2) on Sedimentary Host Rock

Limonite Geode (Ironstone Concretion)

Goethite/Limonite FeO(OH)·nH2O

Red Hematite (Iron Ore)

Hematite (Fe2O3)

Hematite

Iron(III) oxide (Fe2O3)

Limonite (Iron Ore)

Hydrated ferric oxide (FeO(OH)·nH2O)

Magnetite / Ironstone Pebble

Magnetite (Fe3O4)

Iron Ore (Hematite/Goethite)

Ironstone (Fe2O3 / FeO(OH))

Limonite (Iron Ore)

Hydrous Iron Oxide (goethite, lepidocrocite)

Specular Hematite Geode/Nodule

Specularite (Polycrystalline Hematite), Fe2O3

Hematite

Hematite (Fe2O3)

Goethite/Limonite Iron Ore Node

Goethite (FeO(OH)) or Limonite (mixture of hydrated iron oxides)

Hematite

Iron(III) oxide (Fe2O3)

Magnetite / Hematite mix

Magnetite (Fe3O4) and Hematite (Fe2O3)

Banded iron formation (iron-rich metamorphic rock)

Banded iron formation, chiefly hematite/magnetite with chert or quartz (Fe₂O₃/Fe₃O₄ + SiO₂)

Iron-rich slag or limonite-bearing rock

Hydrated iron oxides, chiefly limonite/goethite (FeO(OH)·nH₂O); possibly industrial iron slag

Mahogany Obsidian

Volcanic Glass (SiO2 + Fe2O3)

Hematite

Iron(III) oxide (Fe2O3)

Specular Hematite

Specularite (Iron Oxide, Fe2O3)

Limonite (Yellow Ochre)

Limonite (Hydrated iron(III) oxide-hydroxide, FeO(OH)·nH2O)

Yellow Jasper

Silicon dioxide (SiO2)

Yellow Jasper / Chert

Silicon Dioxide (SiO2) with Goethite or Limonite inclusions