Obsidian with Slate/Tuff
Volcanic glass (SiO2) with associated pyroclastic rock
igneous
Category
Organic (Non Rock)
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Siltstone
Siltstone (fined-grained clastic sedimentary rock)
sedimentary
River Pebble (likely Quartzite or Chert)
Silicon Dioxide (SiO2)
metamorphic or sedimentary
Obsidian
Volcanic Glass (SiO2, usually 70% or more)
igneous
Quartzite
Quartzite (SiO2)
metamorphic
Sandstone
Arenite (Sedimentary rock comprising sand-sized grains)
sedimentary
Conglomerate
Conglomerative Sedimentary Rock
sedimentary
Anthracite Coal
Anthracite
sedimentary
Bituminous Coal
Coal (Organically derived sedimentary rock)
sedimentary
Snowflake Obsidian
Obsidian with Cristobalite inclusions (70–75% SiO2)
igneous
Obsidian
Volcanic Glass
igneous
Basalt River Pebble
Basalt (Mafic Volcanic Rock)
igneous
Shale
Shale (Sedimentary rock composed of mud/clay minerals)
sedimentary
Iron-rich quartzite or quartz-bearing metamorphic rock
Quartzite, predominantly SiO₂, with iron-oxide staining (hematite/goethite)
metamorphic
Chert (Flint)
Microcrystalline Quartz (SiO2)
sedimentary
Quartzite Pebble
Quartzite (primarily SiO2)
metamorphic
Jasper (specifically Polychrome or Desert Jasper)
Silicon Dioxide (SiO2) with iron oxide and other mineral impurities
sedimentary (chemical/biological origin)
Limonite (Iron Ore)
FeO(OH)·nH2O (Hydrated Iron Oxide)
mineral
Fossilized Tooth
Vertebrate Fossilized Tooth (Mineralized Biogenic Material)
fossil
Poppy Jasper
Microcrystalline Quartz (SiO2) with hematite and other inclusions
sedimentary
Chert (Nodule)
Chert (Cryptocrystalline Silica, SiO2)
sedimentary
Quartzite Pebble
Quartzite (composed primarily of SiO2)
metamorphic
Banded Sandstone (Liesegang Rings)
Sedimentary sandstone with Iron oxide precipitates
sedimentary
Sandstone pebble
Sandstone (arenite / quartzarenite)
sedimentary
Granite / Feldspar gravel
Granite (felsic intrusive igneous rock)
igneous
Limestone
Calcium Carbonate (CaCO3)
sedimentary
Fossiliferous Limestone
Sedimentary Calcium Carbonate (CaCO3)
sedimentary
Quartzite
Metamorphic Rock (composed mainly of SiO2)
metamorphic
Limestone Pebble
Sedimentary Rock (Calcite, CaCO3)
sedimentary
Chert (Chert Nodule with Chalky Cortex)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
sedimentary
Siltstone or Fine-grained Sandstone pebble
Siltstone (primarily SiO2 with clay minerals)
sedimentary
Quartzite
Metamorphic Quartz Rock (SiO2)
metamorphic
Quartzite Pebble
Quartzite
metamorphic
Snowflake Obsidian
Volcanic glass containing Cristobalite (SiO2)
igneous
Mahogany Obsidian
Obsidian (Volcanic Glass with Hematite/Magnetite inclusions)
igneous
Quartz Geode
Silicon Dioxide (SiO2)
mineral
Quartzite with Hematite
Metamorphosed Quartz Sandstone (SiO2 with Fe2O3 inclusions)
metamorphic
Quartzite
Quartzite (primarily SiO2)
metamorphic
Blue Slag Glass
Man-made Silicon Dioxide (Amorphous)
Anthropogenic (Man-made)
Obsidian
Volcanic Glass (Amorphous Silicon Dioxide, SiO2)
igneous
Gold Ore in Quartz
Native Gold (Au) in Quartz (SiO2)
mineral
Geode (Unopened)
Silica-rich concretion (SiO2)
sedimentary