Obsidian
Volcanic Glass (70-75% SiO2)
igneous
Category
Organic (Non Geological)
Browse organic (non geological) specimens identified by the Rock Identifier community.
Black tourmaline (likely schorl)
Schorl, NaFe3Al6(BO3)3Si6O18(OH)4
mineral
Green cabochon gemstone pendant
Indeterminate; likely dyed green turquoise, chrysoprase, or opaque beryl set with blue/clear accent stones
gemstone
Rounded sandstone cobble
Clastic sandstone, likely quartz-rich (quartz arenite or arkose)
sedimentary
Snowflake Obsidian
Spherulitic Obsidian (Amorphous volcanic glass with Phenocrysts of Cristobalite)
igneous
Green aventurine (tumbled)
Quartz, SiO₂, with fuchsite or other mica inclusions
mineral
Graphitic schist (probable)
Graphite-bearing mica schist; chiefly quartz, mica, and graphite
metamorphic
Polished quartz-rich pebble, possibly jasper or quartzite
Quartzite or chalcedony-bearing jasper; predominantly SiO₂
metamorphic
Opalite
Opalescent Glass (SiO2 + coloring agents)
Mineral (Synthetic/Man-made)
River Siltstone / Mudstone Pebble
Siltstone (composed of mixed silicate and carbonate minerals)
sedimentary
Green Chert
Microcrystalline Quartz (SiO2)
sedimentary
Polished Black Obsidian
Volcanic Glass (70-75% SiO2)
igneous
Obsidian
Volcanic Glass (SiO2)
igneous
Chert (Concretion or Nodular Variety)
Microcrystalline Quartz (SiO2)
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
fossil
Quartzite
Quartzite (primarily SiO2)
metamorphic
Acrylic or Resin (Synthetic Imitation)
Polymethyl Methacrylate (PMMA) or Polyepoxide
Synthetic/Man-made Polymer
Obsidian
Volcanic Glass (SiO2)
igneous
Mixed gemstone bead bracelet
Likely rose quartz, amethyst, and possibly rhodonite or lepidolite beads
gemstone
Petrified Wood
Silicified wood (primarily Silicon Dioxide, SiO2)
metamorphic
Zebra Rock (Zebra Stone / Ribbon Stone)
Siltstone with Ferruginous Banding (Primarily Quartz, Kaolinite, and Hematite)
sedimentary
Sandstone pebble
Sandstone (arenite / quartzarenite)
sedimentary
Obsidian
Obsidian (Volcanic glass), 70-75% SiO2
igneous
Quartzite
Quartzite (primarily SiO2)
metamorphic
Mixed Gemstone and Mineral Collection
Silicon Dioxide (SiO2) based minerals and others
mineral
Quartzite
Metamorphic Quartz Rock (SiO2)
metamorphic
Quartzite
Quartzite (SiO2)
metamorphic
Rounded pebble, likely quartzite
Quartzite (dominantly recrystallized quartz, SiO₂); identification is uncertain from the image alone
metamorphic
Chert with Limestone Cortex
Silicon Dioxide (SiO2) with Calcium Carbonate (CaCO3)
sedimentary
Ironstone Concretion (Boxwork)
Siderite-Limonite Concretion (FeO(OH)·nH2O)
sedimentary
Coral Fossil (Hexagonaria)
Hexagonaria sp. (Silica-replaced)
fossil
Fossiliferous Sandstone Pebble (with Crinoid / Shell Impression)
Sandstone containing fossiliferous inclusions (SiO2 matrix with calcite/silica cast fossil)
sedimentary
Amber (Copal)
Succiniferous Resin
mineraloid
Fossiliferous Limestone
Biogenic Sedimentary Rock (CaCO3)
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
fossil
Moqui Marbles
Iron Oxide Concretion (Hematite/Goethite)
sedimentary
Fossilized Coral
Cnidaria (Anthozoa), often replaced by Calcium Carbonate (CaCO3) or Silica (SiO2)
sedimentary
Tumbled amber-colored pebble
Likely quartz/chert or iron-stained chalcedony; exact identification requires testing
mineral
Chert (Flint)
Microcrystalline Quartz (SiO2)
sedimentary
Chert (often called Jasper or Flint)
Silicon Dioxide (SiO2)
sedimentary
Fossil-bearing sedimentary rock, possibly fossil wood or bone
Indeterminate silicified/carbonate fossil in sandstone or mudstone
fossil
Chert (Jasper-like Silicate)
Microcrystalline quartz (SiO2)
sedimentary