Organic Gemstone (Not A Rock Or Mineral)

Geode with Quartz Crystal Cavity

Silicon Dioxide (SiO2) in Calcareous/Siliceous Matrix

Turquoise, Pearl, and Coral Necklace

CuAl6(PO4)4(OH)8·4H2O (Turquoise) / CaCO3 (Pearl and Coral)

Petrified Wood

Silicified Wood (primarily SiO2)

Chert (Jasper/Flint Pebble)

Microcrystalline quartz (SiO2)

Dendritic Agate

Chalcedony (SiO2) with manganese/iron oxide inclusions

Basaltic Tuff / Volcanic Breccia

Pyroclastic Breccia / Lithic Tuff

Chert (Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Precious Red Coral

Corallium rubrum (Calcium Carbonate, CaCO3)

Fossilized Horn Coral

Order Rugosa (Rugose Coral)

Moonstone

Orthoclase Feldspar (KAlSi3O8)

Moss Agate and Hematite

Silica (SiO2) with fibrous inclusions of Manganese or Iron; Hematite (Fe2O3)

Tufa (Limestone)

Calcareous Tufa (CaCO3)

Dendritic Agate (Tree Agate)

Chalcedony (Silicon Dioxide, SiO2) with Manganese or Iron Oxide inclusions

Tree Agate (or Moss Agate)

Dendritic Agate (Silicon Dioxide - SiO2)

Chert (specifically Tan/Yellow Chert)

Chert (Microcrystalline or Cryptocrystalline Silica, SiO2)

Chert (Nodule)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Unakite

Epidotized Granite

Natural Pearl (appearing in a jewelry setting)

Calcium Carbonate (mostly Aragonite), CaCO3 with Conchiolin

Shale (sub-type: Carbonaceous Shale)

Lutaceous Sedimentary Rock

Limestone with Quartz/Calcite Veins

Sedimentary Limestone (CaCO3 with SiO2 or CaCO3 intrusions)

Tiger's Eye

Pseudomorph of Quartz after Crocidolite (SiO2)

Sandstone

Arenicola (comprising mostly Quartz, SiO2)

Sandstone (with carbonaceous plant fragments)

Arenite (composed primarily of SiO2)

Pearl

Calcium Carbonate (CaCO3) - Aragonite/Calcite organic gemstone

Smoky Quartz

Silicon Dioxide (SiO2)

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Chert (with Quartz Vein)

Chert (Siliceous sedimentary rock, predominantly Microcrystalline Quartz SiO2)

Chert with Quartz Veining

Silicon Dioxide (SiO2)

Bituminous Coal (with Anthracite or Vitrinite inclusion)

Organic-rich Sedimentary Rock (Carboniferous classification)

Pyrite

Pyrite (FeS2)

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Lake Superior Agate

Banded Chalcedony (Silicon Dioxide / SiO2)

Chert (varietal: Flint/Jasper mix)

Hydrous Silica (SiO2)

Agate Geode Slice (with Druzy Quartz)

Silicon Dioxide (SiO2)

Chert / River Pebble

Silicon Dioxide (SiO2)

Carnelian (Chalcedony)

Silicon Dioxide (SiO2)

Petrified Wood

Silicified wood (Quartz/Chalcedony - SiO2)

Chert / Flint

Cryptocrystalline Quartz (Silicon Dioxide, SiO2)

Geode (Unopened)

Silica-rich concretion (SiO2)

Chert (Nodule)

Silicon Dioxide (SiO2)

Amber (Dark/Black Variety)

Succinite (Resinite), C10H16O

Amber with inclusion

Amber (Fossilized Tree Resin)