Amethyst
Silicon Dioxide (SiO2) with Fe3+ impurities
mineral
Category
Mineraloid (Human Made Geological Specimen)
Browse mineraloid (human made geological specimen) specimens identified by the Rock Identifier community.
Man-made Jewelry (Metal and Glass/Plastic)
Synthetic Alloy and Amorphous Solid (SiO2/Polymer)
not a rock
Chert (potentially Flint or Mudstone)
Microcrystalline Quartz (SiO2)
sedimentary
Horse Chestnut (Buckeye seed)
Aesculus hippocastanum seed
Organic (Non-geological)
Chert (Jasper Variant likely)
Silicon Dioxide (SiO2)
Sedimentary Rock or Mineral (depending on origin and purity)
Calamites Fossil (Horsetail Stem)
Calamites (Genus), part of the class Equisetopsida
sedimentary
Green Sea Glass
Amorphous Silica (man-made glass), SiO2 + additive metal oxides
mineraloid / anthropogenic (man-made origin)
Diamond
Native Carbon (C)
mineral
Opal
Hydrated amorphous silica (SiO2·nH2O)
mineral
Slag
Ferrous Slag (Amorphous calcium-magnesium-aluminum silicates)
igneous (artificial/anthropogenic)
Petrified Wood (Jet or Coalified Wood appearance)
Silicified wood (principally SiO2) or Carbonized Wood
sedimentary
Yellow Chert or Jasper
Silicon Dioxide (SiO2)
sedimentary
Chert (Yellow or Brown Jasper)
Microcrystalline Quartz (SiO2)
sedimentary
Quartzite
Quartzite (SiO2)
metamorphic
Ferruginous Conglomerate (or Iron-Rich Concrete/Slag)
Clastic Sedimentary (Silicon Dioxide/Iron Oxide matrix)
sedimentary
Opal
Hydrated Silica (SiO2·nH2O)
mineral
Coquina
Biogenic Limestone (mostly Calcium Carbonate, CaCO3)
sedimentary
Chert (and Limestone) River Cobble
Microcrystalline Quartz (SiO2) within Calcium Carbonate (CaCO3)
sedimentary
Jet
Lignite (Anthracite-grade compact coal)
sedimentary
Chert (specifically Blue Chert/Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Jasper variety)
Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Chalcedony/Agate)
Microcrystalline Quartz (SiO2)
sedimentary
Diamond in Kimberlite
Diamond (C in Kimberlite Matrix)
igneous
Amber
Amber (C10H16O)
mineral
Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
igneous
Portable Ceramic Space Heater
Polished Acrylonitrile Butadiene Styrene (ABS) Plastic with Ceramic Heating Elements
not a rock (synthetic/industrial object)
Chert (Flint)
Microcrystalline Quartz (SiO2)
sedimentary
Chert (Jasper/Flint variety)
Microcrystalline quartz (SiO2)
sedimentary
Black Obsidian
Volcanic Glass (SiO2 + impurities like Fe3O4)
igneous
Precious Opal
Hydrated Silica (SiO2·nH2O)
mineral
Banded Calcite (often sold as 'Mexican Onyx' or 'Green Onyx')
Calcite (Calcium Carbonate, CaCO3)
Sedimentary
Banded Chert
Silicon Dioxide (SiO2)
sedimentary
Quartz on Sandstone
Silicon Dioxide (SiO2) in Lithic Sandstone
sedimentary
Tektite (likely Australite)
Tektite (no specific chemical formula as it's a natural glass of variable composition, mostly SiO2, Al2O3, FeO, MgO, CaO, K2O, Na2O, TiO2)
Mineral (specifically a mineraloid)
Chert (variations include Flint/Novaculite)
Chert (formula: SiO2)
sedimentary
Amber
Succinite (Organic Mineraloid) - C10H16O
mineral
Chert (Jasper variety)
Silicon Dioxide (SiO2)
sedimentary
Limonite and Goethite encrusted Chert/Ironstone
Hydrated Iron Oxide (FeO(OH)·nH2O) with cryptocrystalline Silica (SiO2)
sedimentary
Opal
Hydrated Silica (SiO2·nH2O)
mineral
Libyan Desert Glass
Impact-melt silica glass (SiO2 + traces of Al, Fe, Ti)
mineral (Tektite/Impactite)
Tektite (Indochinite)
Tektite (High-silica impact glass)
mineraloid
Banded River Cobble with Mafic Dike
Hydrothermally altered Graywacke or Sandstone with Mafic Intrusion
igneous and sedimentary