Organic (Non Rock)

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Mahogany Obsidian

Obsidian (Volcanic Glass) with Hematite/Magnetite inclusions

Ethiopian Fire Opal

Hydrated Silica (SiO2·nH2O)

Quartzite

Quartzite (primarily SiO2)

Shale with Vein Infillings

Shale (a fine-grained clastic sedimentary rock). The veins could be Calcite (CaCO3), Quartz (SiO2), or other minerals.

Snowflake Obsidian

Vitreous volcanic silicate rock (SiO2) with Spherulite inclusions

Limonite-stained Chert

Silicon Dioxide (SiO2) with Hydrated Iron Oxide (FeO(OH)·nH2O)

Conglomerate

Conglomerate (clastic sedimentary rock)

Quartzite

Quartzite (primarily SiO2)

Quartzite Cobble

Quartzite (primarily SiO2)

Chert (Flint variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Brachiopod Fossil in Limestone

Phylum Brachiopoda (likely Order Spiriferida), CaCO3 (Calcite)

Chert (with Quartz Vein)

Chert (Siliceous sedimentary rock, predominantly Microcrystalline Quartz SiO2)

Chert (and Jasper blend)

Chert (Microcrystalline Quartz, SiO2)

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Fossiliferous Limestone (Coquina / Shell Limestone)

Biogenic Limestone (Calcium Carbonate, CaCO3)

Agatized Petrified Wood

Silicon Dioxide (SiO2) - Chalcedony pseudomorph after Wood

Obsidian

Obsidian (principally SiO2)

Travertine

Calcareous Tufa / Travertine (CaCO3)

Red Jasper

Silicon dioxide (SiO2) with iron oxide (Fe2O3) inclusions

Chert (Flint Nodules)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Chert (varietal Chalcedony or Flint)

Silicon dioxide (SiO2) - Microcrystalline Quartz

Chert Pebble

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Obsidian

Obsidian (Volcanic Glass)

Amygdaloidal Rhyolite

Amygdaloidal Rhyolite (Felsic volcanic rock)

Anthracite Coal

Anthracite (Carbon-rich metamorphic sedimentary rock)

Quartzite

Quartzite (primarily SiO2)

Quartzite River Rock

Metamorphic Quartzite (primarily SiO2)

Graphite Schist

C (Carbonaceous Schist)

Yellow Chert

Sedimentary cryptocrystalline quartz (SiO2)

Petrified Wood

Silicified Wood (primarily SiO2)

White Opal (Common)

Hydrated Silica (SiO2·nH2O)

Quartz Vein in Schist

Quartz (SiO2) in Mica Schist

Ferruginous Sandstone (Ironstone)

Arenite with Iron-Oxide Cement (FeO(OH)·nH2O / Fe2O3)

Quartzite Beach Pebble

Quartzite (primarily SiO2)

Emerald in Matrix

Beryl (Be3Al2Si6O18) containing Chromium/Vanadium impurities

Quartzite (Yellow/Tan)

Metamorphic Rock composed of Quartz (SiO₂)

Anthracite Coal

Low-grade metamorphic carbonaceous rock

Snowflake Obsidian

Spherulitic Volcanic Glass (SiO2 + impurities)

Iron Slag (Industrial Byproduct)

Anthropogenic Vitrification Product/Ferrous Slag

Basalt (River or Beach Pebble)

Basalt (Mafic Extrusive Igneous Rock)