Sandstone (with Concretion)
Arenite / Quartzose Sandstone
sedimentary
Limestone
Calcium Carbonate (CaCO3)
Sedimentary
Sandstone or Limestone
Sedimentary Rock
Sedimentary
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Granite Cobble / Rounded Granite River Rock
Granite
Igneous
Sandstone Concretion
Sedimentary concretion
Sedimentary
Pumice or Tufa/Travertine
Pumice (if igneous) or Calcareous Tufa (if sedimentary)
igneous/sedimentary
Quartz with Iron Oxide Inclusions
SiO2 with Fe2O3 impurities
Mineral
Granite
Granite
Igneous
Pyrite in Quartz
FeS2 (Iron Pyrite) with SiO2 (Quartz)
Mineral/Igneous/Hydrothermal
Sandstone or Mudstone
Sedimentary Rock (Sandstone/Mudstone)
sedimentary
Granite
Granite
Igneous
Quartz with Tourmaline Inclusions (Tourmalinated Quartz)
SiO2 with complex borosilicate inclusions
Mineral
Fossiliferous Limestone
Fossiliferous Limestone
sedimentary
Fossilized Coral
Anthozoa (Fossilized)
Sedimentary / Fossil
Agate Nodule / Weathered Chert
SiO2 (Silicon Dioxide - Microcrystalline Quartz)
Sedimentary / Mineral
Fossilized Horn Coral
Rugosa
fossil
Pumice or Scoria
Vesicular volcanic rock
Igneous
Quartz Geode with Calcite
Silicon Dioxide (SiO2) and Calcium Carbonate (CaCO3)
Mineral/Geode
Slag (Industrial)
N/A (Anthropogenic Slag)
industrial by-product
Chert
Silicon dioxide (SiO2)
Sedimentary
Quartz
Silicon dioxide (SiO2)
Mineral
Granite
Granite
Igneous
Sandstone or Limestone
Arenite or Calcareous Sedimentary Rock
Sedimentary
Chert / Flint
Cryptocrystalline quartz (SiO2)
Sedimentary
Chert
Silicon dioxide (SiO2)
Sedimentary
Sandstone or Quartzite
Arenite (if sedimentary) / Quartzite (if metamorphic)
Sedimentary or Metamorphic
Chalcedony (Agatized Coral / Rough Chalcedony Node)
Silicon Dioxide (SiO2)
mineral
Coquina or Fossiliferous Limestone
Fossiliferous Calcarenite (CaCO3)
sedimentary
Geode with Quartz/Chalcedony
Silicon Dioxide (SiO2)
sedimentary
Red Jasper (Chert)
Silicon dioxide (SiO2) with iron oxide inclusions
sedimentary
Sandstone with Algae Growth
Arenite with Chlorophyta/Lichen
sedimentary
Red Quartzite / Ferruginous Sandstone
Quartzite (SiO2 with iron oxide impurities)
metamorphic
Pink Granite
Granite (Phaneritic intrusive rock rich in K-feldspar)
igneous
Carnelian (Carnelian Agate)
Carnelian (Silicon Dioxide - SiO2)
mineral
Amethyst
Amethyst (Silicon Dioxide, SiO2)
mineral
Tiger's Eye
Tiger's Eye (Pseudomorph of Quartz after Crocidolite), SiO2
metamorphic
Sandstone (Quartz Sandstone)
Arenite (primarily SiO2)
sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Anthracite Coal
Anthracite
metamorphic
Sandstone (Ferruginous)
Arenite with Iron Oxide (Limonite/Hematite) coating
sedimentary
Greenstone
Metamorphosed Mafic Igneous Rock
metamorphic