Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
sedimentary
Category
Industrial Byproduct (Often Mistaken For Obsidian Or Mineral)
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Concretion in Shale
Siltstone/Shale with Siderite or Calcareous concretions
sedimentary
Obsidian
Volcanic glass (high silica SiO2)
igneous
Obsidian (Gold Sheen)
Obsidian (SiO2 + impurities)
igneous
Siderite Concretion
Ironstone (Siderite) Concretion, FeCO3
sedimentary
Black Obsidian
Obsidian, SiO2 (amorphous)
Igneous rock (Volcanic glass)
Black Obsidian
Volcanic Glass (SiO2)
igneous
Obsidian
Volcanic Glass (Amorphous Silica)
igneous
Obsidian
Volcanic Glass (predominantly SiO2)
igneous
Amazonite
KAlSi3O8 (Potassium Aluminum Silicate) - a variety of Microcline Feldspar
mineral
Sandstone Concretion
Sandstone (Sedimentary rock, mostly SiO2)
sedimentary
Jasper (Multi-colored) / Sea Glass Slag
Silicon Dioxide (SiO2) with impurities of Iron Oxide
Sedimentary (if natural Jasper) or Artificial (if Slag)
Manganese Dendrite on Siltstone
Manganese Oxide (pyrolusite or psilomelane) Dendrites
mineral/sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Siltstone with iron staining
Siltstone (primarily SiO2 with FeO(OH) coatings)
sedimentary
Mahogany Obsidian
Volcanic glass containing Hematite or Magnetite (SiO2 + Fe2O3)
igneous
Obsidian (likely Golden Sheen Obsidian or Rainbow Obsidian, given the subtle sheen visible on some beads)
Obsidian (volcanic glass, predominantly SiO2 with various impurities)
Igneous
Obsidian
Amorphous volcanic glass (primarily SiO2)
igneous
Silver (Jewelry form)
Native Silver (Ag)
mineral
Mahogany Obsidian
Volcanic Glass with Hematite inclusions (SiO2 + Fe2O3)
igneous
Black Onyx
Silicon Dioxide (SiO2)
mineral
Quartz Pebble (with Manganese dendrites/staining)
Silicon Dioxide (SiO2) with Manganese Oxide impurities
mineral
Obsidian
Obsidian (Volcanic Glass, SiO2 dominated)
igneous
Obsidian
Volcanic Glass (SiO2)
igneous
Asphalt (Aggregate)
Bituminous macadam / Concrete Aggregate
sedimentary
Ironstone concretion
Siderite or Limonite concretion (FeCO3 or FeO(OH)·nH2O)
sedimentary
Perlite (Unexpanded)
Amorphous volcanic glass
igneous
Obsidian
Volcanic Glass (SiO2)
igneous
Obsidian
Volcanic Glass (SiO2 + minor impurities)
igneous
Smoky Quartz
Quartz (SiO₂)
Mineral
Obsidian
Obsidian (Volcanic Glass)
igneous
Ironstone Concretion
Siderite or Hematite-rich Concretion (FeCO3 / Fe2O3)
sedimentary
Blue Apatite
Fluorapatite / Ca5(PO4)3F
mineral
Quartzite
Quartzite (SiO2)
metamorphic
Mahogany Obsidian
Volcanic Glass with Hematite or Magnetite (SiO2 + Fe2O3)
igneous
Sulfur (with possible Cullet Glass or Slag imitation)
Native Sulfur (S8)
mineral
Obsidian
Obsidian (Volcanic Glass)
igneous
Mahogany Obsidian
Volcanic glass (SiO2 + Fe2O3)
igneous
Yellow Jasper with Dendritic Inclusions
Silicon Dioxide (SiO2) with Manganese/Iron Oxide inclusions
sedimentary
Sheen Obsidian
Volcanic glass (SiO2 with inclusions)
igneous
Manganese-coated Sandstone
Clastic sedimentary rock with Manganese Oxide (often Pyrolusite or Psilomelane)
sedimentary
Yellow Aventurine
Quartzite with inclusions (SiO2)
metamorphic