Organic (Non Geological)

Limonite or Ironstone Nodule

FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)

Amber

Succinite (formula varies, primarily C10H16O)

Limestone

Calcium Carbonate (CaCO3)

Garden Pebble (Quartzite or Limestone fragment)

Silicon Dioxide (SiO2) or Calcium Carbonate (CaCO3) fragment

Quartzite Pebble

Metamorphic Quartzite (predominantly SiO2)

Weathered polymictic gravel/conglomeratic rock

Polymictic conglomerate or poorly lithified alluvial gravel; chiefly quartz, feldspar, mica, and dark lithic fragments

Limestone

Calcium Carbonate (CaCO3)

Polished dark gemstone, likely hematite or magnetite

Hematite (Fe₂O₃) or magnetite (Fe₃O₄); exact identification requires testing

Cullet Glass (Slag Glass)

Amorphous Silicon Dioxide (SiO2) with metallic oxide impurities

Blue gemstone bead bracelet, likely dyed agate or another blue stone

Undetermined; possibly dyed chalcedony (microcrystalline quartz, SiO₂)

Rounded iron-rich stone or concretion

Indeterminate; possibly hematite-/goethite-bearing sandstone or an ironstone concretion

Obsidian

Obsidian (Volcanic Glass)

Black Obsidian

Volcanic Glass (SiO2)

Tumbled blue stone, likely sodalite

Sodalite, Na₈(Al₆Si₆O₂₄)Cl₂; identification uncertain from image alone

Fossilized Plant or Tree Bark

Lepidodendron or Sigillaria (example genera)

Petrified Wood

Silicified wood (SiO2)

Slag (Industrial Byproduct)

Ferrous/Non-ferrous Silicate

Black tourmaline pendant

Schorl tourmaline, NaFe3Al6(BO3)3Si6O18(OH)4

Petrified Wood

Silicified wood (primarily Silicon Dioxide, SiO2)

Synthetic Resin (Artificial Specimen)

Polyurethane or Polyester Resin

Small pale rock fragment

Indeterminate; possibly quartz, calcite, or a weathered feldspar-rich fragment

Likely bituminous coal

Coal, predominantly carbon-rich organic matter with variable maceral and mineral content

Weathered ironstone concretion (probable limonite/goethite nodule)

Limonite-goethite-rich iron-oxide concretion; chiefly FeO(OH)·nH₂O

Limonite (with goethite)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

Ferruginous Sandstone Concretion (Ironstone Phosphorite)

Ferruginous Sandstone (variable Fe-oxide/hydroxide composition)

Chert (Jasper/Flint variant)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Chert (variations include Flint)

Silicon Dioxide (SiO2)

Sandstone

Arenite

Black Jasper (Etched)

Silicon Dioxide (SiO2) with impurities

Chert (Flint)

Microcrystalline Quartz (SiO2)

Chert (Flint)

Silicon Dioxide (SiO2)

Chert with Limestone matrix

Microcrystalline silica (SiO2) in Calcite (CaCO3) matrix

Schist with Garnet inclusions

Garnet-mica-schist

Fossiliferous Rock (Invertebrate Fossil in Matrix)

Fossiliferous limestone or shaly matrix containing skeletal fossil remains

Cupronickel (on a 1981 Mexico 20 Pesos coin)

Copper-Nickel Alloy (Cu75Ni25)

Tumbled carnelian (orange chalcedony)

Chalcedony, microcrystalline quartz (SiO₂), colored by iron oxides

Black onyx or black agate bead bracelet

Microcrystalline quartz, chiefly chalcedony (SiO₂); commonly sold as black onyx, sometimes dyed black agate

Chert (Flint variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Jasper

Microcrystalline Quartz (SiO2)

Jasper

Silicon Dioxide (Microcrystalline Quartz, SiO2)

Jasper

Silicon dioxide (SiO2)