Not A Natural Rock (Man Made Composite)

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Tumbled basalt (likely)

Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, often with minor olivine and iron oxides

Blue Sapphire

Corundum (Al2O3) with traces of Iron and Titanium

River Cobble (Diorite or Meta-volcanic with Quartz Veining)

Diorite (with SiO2 quartz veins)

Likely basaltic rock fragment

Fine-grained mafic igneous rock, probably basalt (plagioclase–pyroxene ± olivine)

Banded Sandstone (Liesegang Rings)

Arenite with Liesegang rings (SiO2/Fe2O3)

Limonite (Ochreous Sandstone)

Hydrous ferric oxides (FeO(OH)qnH2O)

Granite

Phaneritic Igneous Rock (primarily Quartz, Feldspar, and Mica)

River Cobble (Quartzite or Gneiss)

Metamorphic crystalline rock (predominantly SiO2 based)

Limonite (with Goethite/Hematite glaze)

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

Dalmatian Stone (Dalmation Jasper)

Aplite with Arfvedsonite inclusions

Clear Quartz Sphere

Crystalline Silicon Dioxide (SiO2)

Sandstone

Arenite (SiO2 based with various mineral cements)

Sandstone (Wonderstone)

Silicified Sandstone / Orthoquartzite with Liesegang rings

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Sandstone

Clastic sedimentary rock (primarily quartz arenite)

Sandstone

Sedimentary Rock (Quartz arenite)

Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Chert (often called Jasper or River Rock)

Chert (SiO2)

Citrine (Heat-Treated Amethyst)

Silicon Dioxide (SiO2)

Red Quartzite River Pebble

Quartzite (SiO2 with iron oxide inclusions)

Turquoise

Hydrated phosphate of copper and aluminum, CuAl6(PO4)4(OH)8·4H2O

Quartz Geode

Silicon Dioxide (SiO2) in sedimentary host rock

Smoky Quartz on Feldspar (Granite Pegmatite)

Silicon Dioxide (SiO2) with Potassium Aluminum Silicate (KAlSi3O8)

Quartz Pebble / Quartzite Pebble

SiO2 (Silicon Dioxide)

Yellow Quartz Pebble

Silicon Dioxide (SiO2)

Jasper

Silicon dioxide (SiO2) with impurities

Ironstone Pebble

Sedimentary ironstone / Hematitic Sandstone

Rough Amethyst

Silicon Dioxide (SiO2) with iron impurities

Agate (Chalcedony)

Silicon Dioxide (SiO2)

Sandstone (Micaceous/Feldspathic variant)

Arenite (specifically subarkose or lithic arenite)

Herkimer Diamond

Quartz (Silicon Dioxide, SiO2)

Basalt and weathered granite-like rock

Dark specimen: basalt, likely vesicular or fine-grained mafic volcanic rock; tan specimen: uncertain, possibly weathered granite or iron-stained felsic rock

Conglomerate

Clastic sedimentary rock (Puddingstone)

Red Sandstone

Arenite (Ferruginous Sandstone)

Shale fragment

Shale (Laminated Mudstone)

Quartz Pebble

Silicon Dioxide (SiO2)

White quartz in dark matrix (likely quartz-bearing breccia or polished composite specimen)

Quartz, SiO₂, in an unidentified dark silicate matrix

Iron-rich weathered rock, likely limonite/goethite-bearing laterite

Limonite (variable hydrated iron oxides; chiefly goethite, α-FeO(OH))

Amethyst (Tumbled)

Amethyst (Silicon Dioxide, SiO2 + Fe4+)

Sandstone (likely Siltstone or fine-grained Sandstone)

Sedimentary Rock (Clastic)

Red jasper-like chalcedony pebble

Microcrystalline quartz (SiO₂), likely iron-stained chalcedony/jasper