Sedimentary Rock (Specifically A Concretion Or Possibly A Geode)

Quartz-bearing gray rock, likely druzy quartz in host rock

Quartz (SiO₂), possibly in a chert, chalcedony, or fine-grained volcanic host

Amethyst (Chevron Amethyst)

Amethystine Quartz (SiO2)

Ironstone Concretion (Moqui Marble variety)

Ferruginous Sandstone Concretion

Ironstone concretion with iron-oxide/possibly hematite inclusions

Ferruginous sandstone or lateritic ironstone; inclusions likely hematite (Fe₂O₃) and/or goethite (FeO(OH))

Weathered limestone fragment, possibly fossiliferous

Calcite-rich limestone (CaCO₃); exact identification is uncertain from one image

Ironstone Concretion

Limonitic/Hematitic Concretion

Green Druzy Quartz (Prasiolite)

Silicon Dioxide (SiO2) with inclusions (typically Chlorite or Actinolite)

Vuggy quartz-rich rock, possibly quartzite or quartz geode

Microcrystalline to crystalline SiO₂ (quartz), likely quartzite with a small quartz-lined vug

Sandstone Concretion

Sandstone (Sedimentary rock, mostly SiO2)

Ironstone Concretion

Siderite / Hematite-bearing Sedimentary Rock

Sandstone Concretion

Clastic Sedimentary Rock - Quartz Arenite / Sandstone

Geode Nodule Fragment

Quartz / Chalcedony Nodule

Limestone (specifically Dolomitic Limestone)

Calcium Magnesium Carbonate (CaMg(CO3)2)

Sandstone Concretion

Clastic sedimentary rock (primarily Quartz SiO2 with mineral cement)

Botryoidal chalcedony (possibly quartz geode coating)

Microcrystalline quartz, SiO₂; botryoidal chalcedony

Limonite Concretion

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

Chert Concretion

Microcrystalline Quartz (SiO2)

Quartz Geode

Silicon Dioxide (SiO2)

Ironstone concretion (likely limonite/goethite-rich)

Iron-oxide-cemented sediment, commonly goethite (FeO(OH)) and/or limonite

Geode (Quartz / Chalcedony Geode)

Silicon Dioxide (SiO2) - Quartz / Chalcedony

Blue-gray flint (chert) fragment

Microcrystalline quartz (SiO₂), commonly called flint or chert

Geode (Unopened)

Crystalline Quartz or Chalcedony filled Geode (SiO2)

Omarolluk (Omar)

Siliceous greywacke concretion

Amethyst cluster

Amethyst, purple quartz (SiO₂)

Gneiss (specifically a weathered Amphibolite or Garnet Gneiss)

Gneiss (complex silicate composition)

Likely weathered limestone

Calcite-rich limestone (mostly CaCO₃), possibly dolomitic limestone

River Rocks and Pebbles

Mixed Silica-rich Sediments (SiO2 based)

Ironstone Concretion

Siderite or Limonite Concretion

Quartz (Druzy)

Silicon Dioxide (SiO2)

Banded Agate (specifically Carnelian Agate slice)

Chalcedony (cryptocrystalline variety of Quartz), SiO2

Septarian Nodule Geode

Septarian concretions (composed of Calcite, Aragonite, and Limestone)

Chert Concretion

Sedimentary Cryptocrystalline Quartz (SiO2)

Gneiss (specifically Micaceous Gneiss)

Gneiss (High-grade Regional Metamorphic Rock)

Quartz Geode

Silicon Dioxide (SiO2)

Quartz Geode Fragment

Silicon Dioxide (SiO2)

Chalcedony Geode Fragment

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Ironstone Concretion

Ferruginous Concretion (Fe2O3·nH2O)

Ironstone Concretion

Ironstone (Limonite/Goethite/Hematite mixture)

Ironstone Concretion

Ferruginous Sandstone / Iron-rich Sedimentary Rock

Quartz Geode

Silicon Dioxide (SiO2) in a concretionary structure

Agate (specifically Chalcedony/Banded Agate)

Silicon Dioxide (SiO2)

Ironstone Nodules (Iron Concretion)

Siderite or Hematite Concretion