Septarian Nodule (Dragon Stone)
Septarian Nodule (Calcium Carbonate/Aragonite/Calcite Concretion)
sedimentary
Category
Not A Geological Specimen
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Petrified Wood
Silicified Wood (SiO2)
sedimentary
Auriferous Quartz (Gold-bearing Quartz)
Silicon Dioxide (SiO2) with trace Gold (Au) and Iron Oxides
mineral
Banded Iron Formation (Fragment)
Banded Iron Formation (BIF)
sedimentary
Siderite Concretion in Shale
Iron carbonate (FeCO3) in Mudstone/Shale matrix
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
fossil
Tektite (Indochinite)
Impact Glass (SiO2 + Al2O3)
mineraloid
Moqui Marble (Shaman Stone)
Iron Oxide Concretion (Hematite/Goethite)
sedimentary
Terrazzo flooring containing marble aggregate
Marble (recrystallized calcite, CaCO₃) aggregate in cementitious terrazzo
metamorphic
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Devil's Toenail
Gryphaea (extinct genus of foam oysters, typically composed of Calcite CaCO3)
sedimentary
Limonite (Yellow Ochre)
Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)
mineral
Favosites Fossil (Honeycomb Coral)
Favosites alpenensis (Order: Tabulata)
fossil
Fulgurite
Fulgurite (Lechatelierite-rich fused silica)
mineraloid / sedimentary (secondary formation)
Limonite or Ironstone Nodule
FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)
sedimentary
Black basalt pebble
Basalt; fine-grained mafic volcanic rock, commonly composed of plagioclase, pyroxene, and minor olivine or magnetite
igneous
Fossil Coral (Tabulate Coral Fragment)
Anthopleura / Tabulata (CaCO3 - Calcium Carbonate)
fossil
Limonite and Goethite encrusted Chert/Ironstone
Hydrated Iron Oxide (FeO(OH)·nH2O) with cryptocrystalline Silica (SiO2)
sedimentary
Basalt
Basalt (dominated by Plagioclase Feldspar and Pyroxene)
igneous
Quartzite
Quartzite (SiO2)
metamorphic
Rounded gray pebble
Unidentified lithic pebble; likely quartz-rich sandstone, quartzite, or fine-grained igneous rock
sedimentary
Chert / Flint Nodule
Microcrystalline Quartz (SiO2)
sedimentary
Dark gray slate or phyllite cobble
Slate–phyllite, composed mainly of fine-grained mica, quartz, and chlorite
metamorphic
Chert (Pink Jasper)
Microcrystalline Quartz (SiO2)
sedimentary
Conglomerate
Conglomerate Rock
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
sedimentary
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Milky Quartz (Gold-bearing Prospecting Specimen)
Silicon Dioxide (SiO2)
mineral
Quartz Pebble in Sandstone matrix
Quartz Conglomerate (SiO2 matrix)
sedimentary
Quartz-veined Metamorphic Rock
Quartz-veined Schist or Gneiss
metamorphic
Quartz Breccia with Iron Staining
Tectonic or Sedimentary Breccia (SiO2 with Fe2O3)
sedimentary
Banded Iron Formation (BIF) / Banded Sandstone Nodule
Hematite-rich Sandstone / Ferruginous Chert
sedimentary
Banded gneiss pebble
Gneiss, composed chiefly of quartz, feldspar, and mica/amphibole
metamorphic
Granite Pegmatite with Muscovite Mica
Granite Pegmatite (Silicon Dioxide and complex silicates)
igneous
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Glacial erratic boulder
Likely weathered sandstone or quartzitic sandstone; exact identification requires a fresh surface and locality
sedimentary
Fulgarite
Fulgurite (Lechatelierite / Vitrified Sand)
igneous
Fossil Coral
Hexagonaria or Rugose coral fossil in limestone/silica matrix
fossil
Quartzite with Mafic Intrusion (Gneiss/Schist Contact)
Metamorphic Quartzite (SiO2) with Amphibole/Biotite Schist
metamorphic
One Pound Coin (UK)
Nickel-Brass Alloy (Cu-Zn-Ni)
mineral
Weathered sandstone pebble
Quartz-rich sandstone, likely arkosic or lithic sandstone
sedimentary
Banded Calcite (often commercially called 'Mexican Onyx')
Calcium Carbonate (CaCO3)
mineral