Tree Agate (also known as Dendritic Agate)
Silicon Dioxide with inclusions (SiO2 + Mn/Fe)
mineral
Category
Organic (Often Found By Beachcombers)
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Amber (Black)
Amber (succinite, retinite, etc., specifically, heavily included/dark varieties)
Mineraloid
Petrified Wood
Silicified Wood (SiO2 - Silicon Dioxide)
mineral
Petrified Wood
Silicified Wood (SiO2 - Silicon Dioxide)
mineral
Gastropod Fossil (Internal Mold)
Phylum Mollusca, Class Gastropoda (Steinkern)
sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
sedimentary
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Black Limestone with Calcite Veins
Limestone (Calcium Carbonate, CaCO3)
sedimentary
Chert (variations include Flint)
Chert (SiO2)
sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Amber
Succinite
mineral
Amber
Succinite (fossilized resin)
mineral
Blue Apatite
Apatite, Ca5(PO4)3(F,Cl,OH)
mineral
Amber
Succinite
Organic Mineral
Pearl
Calcium Carbonate (Aragonite/Calcite) with Conchiolin (CaCO3)
mineral
Fossilized Plant or Tree Bark
Lepidodendron or Sigillaria (example genera)
sedimentary
Ironstone Concretion / Limonite Node
Ferruginous Sedimentary Rock (composed primarily of Limonite FeO(OH)·nH2O and Goethite)
sedimentary
Amber
Succinates (C10H16O)
mineraloid
Chert (Arrowhead Artifact)
Chert (SiO2)
sedimentary
Fossiliferous Limestone
Calcium Carbonate (CaCO3) with Bioclastic Inclusions
sedimentary
Nacre (Mother of Pearl)
Nacre (Biogenic Aragonite/Calcite composite, CaCO3)
mineral
Pearl
Aragonite (CaCO3 with conchiolin)
mineral
Baroque Pearl
Calcium Carbonate (Aragonite or Calcite) and Conchiolin
Organic Gemstone
Fossil Shark Tooth
Otodus sp. or Carcharocles sp. (likely fossilized Chondrichthyes)
fossil
Banded Siltstone Pebble
Siltstone (primarily SiO2, Al2O3, Fe2O3)
sedimentary
Red Coral
Corallium rubrum (Calcium Carbonate, CaCO3 with Carotenoid pigments)
Mineraloid (Organic Gemstone)
Petrified Wood
Silicified Wood (primarily SiO₂ - Silicon Dioxide)
metamorphic
Chert (Jasper variation)
Microcrystalline Quartz (SiO2)
sedimentary
Fossilized Shark Tooth
Carcharocles or Otodus sp. (Micro-fossilized)
sedimentary
Coquina or Fossiliferous Limestone
Fossiliferous Calcarenite (CaCO3)
sedimentary
Natural White Pearl
Calcium Carbonate (Aragonite/Calcite) with Conchiolin - CaCO3
mineraloid
Fossilized Fish Skeleton in Matrix
Vertebrata (Class: Actinopterygii), typically found in limestone or shale matrices
sedimentary
Amber
Succinite
Organic Gemstone (sedimentary associations)
Banded Chert
Microcrystalline Quartz (SiO2)
sedimentary
Limestone with Lichen/Moss
Calcium Carbonate (CaCO3)
sedimentary
Green Moss Agate
Agate (Silicon Dioxide, SiO2) with inclusions of hornblende or chlorite
mineral
Pyrite
Pyrite (Iron Disulfide), FeS2
Mineral
Glauconitic Sandstone
Glauconitic Quartz Arenite
sedimentary
Chert
Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
sedimentary
Precious Red Coral
Corallium rubrum (Calcium Carbonate, CaCO3)
mineral
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary