Natural Pearl
Calcium carbonate (primarily Aragonite and Conchiolin), CaCO3
mineral
Category
Organic (Often Found By Beachcombers)
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Chert (Quartz Pebble)
Silicon Dioxide (SiO2)
sedimentary
Dendritic Agate (or Dendritic Opal)
SiO2 (for Agate), SiO2·nH2O (for Opal)
Mineral
Black Limestone with Calcite Veining
Bituminous Limestone (CaCO3 with Organic Carbon inclusions)
sedimentary
Limestone with Quartz/Calcite Veins
Sedimentary Limestone (CaCO3 with SiO2 or CaCO3 intrusions)
sedimentary
Chert (and/or Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
sedimentary
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Amber (Rough)
Amber (Fossilized Tree Resin, succinite)
mineral
Pink Opal (Common Opal)
Amorphous Hydrated Silica (SiO2·nH2O)
mineral
Jasper (Petrified Wood variant)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
sedimentary
Chert (Flint Pebbles)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Amber
Succinite
mineral
Jasper (specifically Yellow Jasper and Red Jasper)
Silicon Dioxide (SiO2) with iron oxide inclusions
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2 - Silicon Dioxide)
sedimentary
Travertine (Tufa)
Travertine (Aragonite/Calcite form of Calcium Carbonate, CaCO3)
sedimentary
Petrified Wood
Silicified Wood (SiO2)
sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
sedimentary
Fossilized Wood (with Coal and Limonite)
Petrified Wood (Silicified or Carbonized Flora)
sedimentary
Banded Chert (Ironstone/Jasper)
Cryptocrystalline Quartz (SiO2) with Iron Oxides
sedimentary
Septarian Nodule
Septarian Concretion
sedimentary
Pyrite (Fool's Gold)
Iron Sulfide (FeS2)
mineral
Sandstone (Ferruginous)
Clastic Sedimentary Rock (Sandstone)
sedimentary
Chert (within Asphalt)
Chert (SiO2)
sedimentary
Chert (Flint) with Limestone Matrix
Silicon Dioxide (SiO2) within Calcium Carbonate (CaCO3)
sedimentary
Travertine (Tufa)
Chemical Sedimentary Rock (CaCO3)
sedimentary
Sea Glass (specifically Frosted White)
Amorphous Silica (substance: Sodium-calcium silicate glass)
Mineraloid (Anthropogenic/Man-made rock)
Shale with Vein Infillings
Shale (a fine-grained clastic sedimentary rock). The veins could be Calcite (CaCO3), Quartz (SiO2), or other minerals.
Sedimentary Rock
Chert with Quartz Veining
Silicon Dioxide (SiO2)
sedimentary
Chert (Field Stone)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
sedimentary
Amber (specifically Cherry Amber)
Succinite (with the chemical formula C10H16O)
Organic Gemstone (not a mineral)
Chert (often called Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Ironstone Concretion (Limonite/Hematite Nodules)
Ironstone (principally Limonite FeO(OH)·nH2O or Hematite Fe2O3 mixed with silica/clay)
sedimentary
Chert (Iron-stained)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (variously known as Flint or Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
sedimentary
Petrified Wood (Agatized/Silicified Wood)
Silicified Wood / Chalcedony (SiO2)
sedimentary
Moss Agate with Quartz Druzy
Chalcedony with inclusions (SiO2)
mineral
Moss Agate
Chalcedony (Silicon Dioxide with inclusions) - SiO2
mineral
Quartz Geode
Silicon Dioxide (SiO2)
mineral
Chert Pebble (with Quartz Vein)
Chert (Cryptocrystalline Silica - SiO2)
sedimentary
Chert (often called Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Cherty Flint/Jasper variety)
Microcrystalline or cryptocrystalline Quartz (SiO2)
sedimentary