Sandstone Concretion
Clastic sedimentary rock (primarily Silica, SiO2, or Calcium Carbonate, CaCO3)
sedimentary
Category
Industrial Byproduct (Often Mistaken For Obsidian Or Mineral)
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Specular Hematite (Specularite) in Matrix
Specularite (Fe2O3)
mineral
Mahogany Obsidian
Volcanic glass containing Magnetite/Hematite
igneous
Concretion (Sandstone)
Carbonate-cemented Sandstone Concretion
sedimentary
Obsidian
Volcanic Glass (SiO2 rich)
igneous
Obsidian
Volcanic glass (SiO2 + impurities)
igneous
Obsidian
Extrusive igneous volcanic glass
igneous
Chert (Flint)
Chert (SiO2)
sedimentary
Iron Concretion
Ferruginous concretion (Fe2O3·nH2O / FeO(OH))
sedimentary
Apatite
Apatite Group (e.g., Fluorapatite Ca5(PO4)3F, Chlorapatite Ca5(PO4)3Cl, Hydroxylapatite Ca5(PO4)3(OH))
mineral
Sandstone with Liesegang Rings
Clastic Sedimentary Rock with Iron Oxide Precipitates (SiO2 + Fe2O3)
sedimentary
Blue Dumortierite Quartz
Dumortierite Inclusions in Quartz (SiO2 with Al7(BO3)(SiO4)3O3)
mineral
Obsidian
Obsidian (principally SiO2 + MgO, Fe3O4)
igneous
Obsidian
Obsidian (Volcanic Glass, SiO2 + impurity)
Igneous
Variscite in Matrix
Variscite (AlPO4 · 2H2O)
mineral
Sandstone (with Concretion)
Arenite / Quartzose Sandstone
sedimentary
Yellow Aventurine
Quartz containing Muscovite or Mica inclusions (SiO2)
mineral
Snowflake Obsidian
Volcanic glass with Cristobalite inclusions (70–75% SiO2)
igneous
Obsidian
Volcanic Glass (SiO2 + impurities)
igneous
Concretion
Sedimentary Concretion (e.g., Siderite or Ironstone)
sedimentary
Mahogany Obsidian
Volcanic Glass (with inclusions of Magnetite or Hematite)
igneous
Taaffeite
BeMgAl4O8 (Beryllium Magnesium Aluminum Oxide)
mineral
Mahogany Obsidian
Obsidian (Volcanic Glass) with Hematite/Magnetite inclusions
igneous
Tiffany Stone
Bertrandite Fluorite (CaF2 + Be4Si2O7(OH)2)
metamorphic
Obsidian
Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide)
igneous
Sandstone Concretion
Clastic sedimentary rock (primarily Quartz SiO2 with mineral cement)
sedimentary
Milky Quartz with Iron Staining
Silicon Dioxide (SiO2)
mineral
Obsidian
Obsidian (Volcanic Glass, ~70% SiO2)
igneous
Quartzite River Rock with Dendrites
Metamorphosed Quartz-rich Sandstone with Manganese Oxide (MnO2) inclusions
metamorphic
Obsidian
Obsidian (Volcanic Glass, complex silicate)
igneous
Obsidian
Volcanic Glass (Amorphous Silica, SiO2)
igneous
Quartz
Silicon Dioxide (SiO2)
mineral
Obsidian
Amorphous volcanic glass (70-75% SiO2)
igneous
Sandstone Concretion
Septarian or Carbonate-cemented Sandstone Concretion
sedimentary
Mahogany Obsidian
Volcanic Glass (predominantly SiO2 with Fe2O3 inclusions)
igneous
Pyrite in Quartzite/Graphite Matrix
Iron Sulfide (FeS2)
Mineral
Boxwork Siderite or Sepatarian Nodule Weathering
Siderite (FeCO3) with secondary mineralization or Boxwork Geode fragment
sedimentary
Obsidian
Volcanic Glass (SiO2)
igneous
Scoria with Calcite Infills
Vesicular Basalt with secondary Calcification (CaCO3)
igneous
Obsidian
Volcanic Glass (SiO2 rich)
igneous
Obsidian
Volcanic Glass (Amorphous Silica)
igneous
Sandstone Concretion
Clastic Sedimentary Concretion (primarily SiO2 with Fe2O3 cement)
sedimentary