Chert (often called Flint)
Chert (Cryptocrystalline Quartz, SiO2)
sedimentary
Black Obsidian
Volcanic Glass (SiO2)
igneous
Sandstone
Arenite (SiO2 based)
sedimentary
African Turquoise
African Turquoise (a trade name for Jasper, a variety of Chalcedony: SiO2)
sedimentary
Chert
Chert (SiO2)
sedimentary
Basalt River Stone
Aphanitic Mafic Igneous Rock
igneous
Gray Agate with Druzy Quartz Geode
Cryptocrystalline Quartz (SiO2)
mineral
Labradorite
(Ca, Na)(Al, Si)4O8
mineral
Tiger's Eye
Pseudomorph of Quartz after Crocidolite (SiO2 with iron inclusions)
metamorphic
Gold Sheen Obsidian
Volcanic Glass (Amorphous Silica with Magnetite inclusions)
igneous
Pink Opal
Amorphous Hydrous Silica (SiO2·nH2O)
mineral
Sodalite in Matrix (Sunset Sodalite)
Sodalite Na8(Al6Si6O24)Cl2
mineral
Dalmatian Stone
Peralkaline rhyolite
igneous
Picture Jasper
Silicon dioxide (SiO2)
sedimentary
Map Jasper (Grey Picasso Jasper)
Silicon Dioxide (SiO2) with impurities
sedimentary
Basalt
Basalt (composition predominately Plagioclase feldspar and Pyroxene)
igneous
Banded Chert
Microcrystalline Quartz (SiO2)
sedimentary
Chert Nodule in Limestone
Chert (Microcrystalline Quartz, SiO2) and Limestone (Calcium Carbonate, CaCO3)
sedimentary
Pegmatite with Muscovite
Granitic Pegmatite (KAl2(AlSi3O10)(OH)2)
igneous
Mica-rich Pegmatite
Pegmatite (rich in Muscovite and Biotite)
igneous
Diorite
Phaneritic Intermediate Igneous Rock
igneous
Aura Quartz Geodes (Lab-Altered)
Silicon Dioxide (SiO2) with Metallic Vapor Deposition
mineral
Dyed Alum or Dyed Quartz (Ornamental Crystal)
Silicon Dioxide (SiO2) or Potassium Alum [KAl(SO4)2·12H2O]
mineral
Sodalite
Sodalite (Na8(Al6Si6O24)Cl2)
mineral
Gneiss
Gneiss
metamorphic
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Granite Pebble
Phaneritic Felsic Igneous Rock
igneous
Chert (Jasper variation)
Chert (Microcrystalline Silicon Dioxide, SiO2)
sedimentary
Limestone
Calcium Carbonate (CaCO3)
sedimentary
Chert (variations include Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
sedimentary
Chert (Tan/Brown variety)
Chert (Microcrystalline Quartz, SiO2)
sedimentary
Chert (Brown Variety)
Microcrystalline quartz (SiO2)
sedimentary
Gneiss
Gneiss
metamorphic
Quartzite
Quartzite (SiO2)
metamorphic
Amethyst Geode
Amethyst (Silicon Dioxide, SiO2)
mineral
Amethyst Geode
Silicon dioxide (SiO2) with iron impurities
mineral
Parti Sapphire
Corundum (Al2O3)
mineral
Fossilized Brachiopod
Phylum Brachiopoda (replaced by Calcite/CaCO3)
sedimentary
Tumbled Stones (various)
Mixed Silica-based Minerals (primarily Quartz and Chalcedony)
mineral
Picture Jasper
Tectonically broken chalcedony (SiO2)
sedimentary
Epidote in Quartz (Epidosite)
Epidote (Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))
metamorphic
Banded Agate (Botswana Agate)
Silicon Dioxide (SiO2)
mineral