Basalt

Granite

Felsic Plutonic Rock (primarily Quartz, Potassium Feldspar, and Plagioclase)

River Cobble (Basaltic/Andesitic)

Mafic to Intermediate Volcanic Rock

Agate

SiO2 (Silicon dioxide, chalcedony variety)

Blue Sapphire

Corundum (Al2O3) with traces of Iron and Titanium

Blue Sapphire

Corundum (Al2O3) with traces of Iron and Titanium

Carnelian Agate

Carnelian (Silicon Dioxide - SiO2)

Banded Agate (specifically Lake Superior Agate type)

Silicon Dioxide (SiO2) - variety Chalcedony

Blue Lace Agate (often dyed)

Silicon dioxide (SiO2) - variety of chalcedony

Bloodstone (also known as Heliotrope)

Silicon Dioxide (SiO2) - variety of Chalcedony

Dyed Agate

Silicon Dioxide (SiO2) - variety Chalcedony

Banded Agate (Lake Superior Agate variant)

Silicon Dioxide (SiO2)

Agate (specifically Carnelian Agate or Sardagate)

Silicon dioxide (SiO2) - variety of chalcedony

Peridot

Olivine ((Mg, Fe)2SiO4)

Banded Agate (Lake Superior Agate style)

Cryptocrystalline Quartz (SiO2)

Carnelian Agate

Silicon Dioxide (SiO2) with iron oxide impurities

Amethyst

Amethyst (Silicon Dioxide - SiO2 with ferric iron impurities)

Larimar

Pectolite [NaCa2Si3O8(OH)] with copper substitution

Chalcedony (Agate)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Amethyst

SiO2 (Silicon Dioxide)

Amethyst (Tumbled)

Silicon Dioxide (SiO2) with iron impurities

Sunstone

Aventurine Feldspar ((Ca,Na)(Al,Si)4O8)

Amethyst

Amethyst (SiO2 with Iron impurities)

Amethyst

Silicon Dioxide (SiO2) with trivalent iron (Fe3+) impurities

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurities)

Scoria (Lava Rock)

Scoria (highly vesicular extrusive igneous rock)

Dolomite on Prehnite (Saddle-shaped Dolomite)

Dolomite [CaMg(CO3)2] on Prehnite [Ca2Al(AlSi3O10)(OH)2]

Olivine-bearing Basalt / Scoria

Mafic Igneous Rock (primarily (Mg, Fe)2SiO4)

Blue Chalcedony

Silicon Dioxide (SiO2)

Blue Chalcedony Geode (with Quartz Druzy)

Silicon Dioxide (SiO2) - Microcrystalline variety of Quartz

Agate Geode Node

Cryptocrystalline Quartz (SiO2)

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Bauxite

Bauxite (mixture including Gibbsite Al(OH)3, Boehmite γ-AlO(OH), and Diaspore α-AlO(OH))

Amethyst

Silicon Dioxide (SiO2) with trace Iron (Fe3+)

Stony-Iron Meteorite (likely Mesosiderite or Ordinary Chondrite)

Meteorite (Silicate-Metal Matrix)

Rhyolite

Rhyolite (Extrusive Igneous Rock)

Moss Agate

Chalcedony (SiO2) with dendritic inclusions of Manganese or Iron oxide

Ruby

Corundum (mineral species), variety: Ruby (Al2O3 with Cr3+ as the chromophore)

Ruby

Corundum (Al2O3:Cr)

Pink Sapphire

Corundum (Al2O3 with trace Chromium and Iron)

Amethyst Quartz

Silicon Dioxide (SiO2 with iron impurities)

Agate (Dyed High-Grade Polished Slice)

Silicon dioxide (SiO2), Chalcedony crystal variety

Amethyst

Silicon Dioxide (SiO2) with iron impurities