Chert (Nodule)
Silicon Dioxide (SiO2)
sedimentary
Category
None
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Sandstone (with differential weathering)
Arenite / Quartz Sandstone (SiO2)
sedimentary
Chert (containing Fossil Mold)
Silicon dioxide (SiO2)
sedimentary
Amethyst
SiO2 (Silicon Dioxide with iron impurities)
mineral
Chert (Flint)
Silicon Dioxide (SiO2)
sedimentary
Orange Quartz (Tangerine Quartz)
Silicon Dioxide (SiO2) with Hematite inclusions
mineral
Quartzite
Quartzite (SiO2)
metamorphic
Red Sandstone
Clastic Terrigenous Sedimentary Rock (primarily SiO2 with Fe2O3 coating)
sedimentary
Jasper with Hematite inclusions
Silicon Dioxide (SiO2) with Ferric Oxide (Fe2O3)
sedimentary
Iron-stained quartz-bearing rock
Quartz-rich limonite/goethite specimen; exact identification requires testing
mineral
Obsidian
Volcanic Glass (SiO2, usually >70% silica content)
Igneous
Picture Jasper
Impure variety of silica (SiO2)
sedimentary
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Limonite (Ironstone Concretion)
Limonite (FeO(OH)·nH2O)
sedimentary
Polished Ocean Jasper
Orbicular Jasper (variety of Chalcedony/Quartz, SiO2)
mineral
Quartzite pebble
Quartzite (SiO2)
metamorphic
Quartzite River Cobble
Quartzite (SiO2)
metamorphic
Snowflake Obsidian
Volcanic Glass with Spherulite inclusions (SiO2)
igneous
Black Obsidian
Volcanic Glass (SiO2 + MgO / Fe3O4)
igneous
Snowflake Obsidian
Volcanic Glass with Spherulite inclusions (Amorphous SiO2 + Cristobalite)
igneous
Black Obsidian
Volcanic Glass (SiO2 + impurities)
igneous
Quartzite River Rock
Metamorphic Quartzite (SiO2)
metamorphic
Quartzite
Quartzite (primarily SiO2)
metamorphic
Siltstone
Siltstone (composed of microscopic quartz and clay minerals)
sedimentary
Quartzite
Quartzite (primarily SiO2)
metamorphic
Quartzite cobblestone
Quartzite (primarily SiO2)
metamorphic
Riverstone Quartzite (Iron-stained)
Quartzite (primarily SiO2 with Limonite/Goethite staining)
metamorphic
Quartzite Pebble
Quartzite (mostly SiO2)
metamorphic
Obsidian (Black)
Obsidian (High-silica volcanic glass)
igneous
Green Slag Glass
Cullet (Amorphous Silicon Dioxide with impurities)
Man-made rock-like material
Black Obsidian
Volcanic Glass (SiO2 + impurities)
Igneous
Quartzite
Quartzite (SiO2)
metamorphic
Quartzite
Quartzite (mostly SiO2)
metamorphic
Quartzite
Quartzite (SiO2)
metamorphic
Quartzite (Orthoquartzite)
SiO2 (Silicon Dioxide) with Iron Oxide inclusions
metamorphic
Mahogany Obsidian
Volcanic glass (SiO2 with Hematite or Magnetite inclusions)
igneous
Blue Quartzite (River Pebble)
Quartzite (primarily SiO2 with Dumortierite or Crocidolite inclusions)
metamorphic
Quartzite
Quartzite (SiO2 silicon dioxide)
metamorphic
Limestone
Calcium Carbonate (CaCO3)
sedimentary
Blue Slag Glass
Anthropogenic Amorphous Silicon Dioxide
mineral
Milky Quartz
SiO2
mineral
Quartzite pebble
Quartzite (SiO2)
metamorphic