Organic Gemstone (Not A Mineral)

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Variscite in Matrix

Variscite (AlPO4 · 2H2O)

Ironstone Concretion

Siderite or Hematite Concretion

Moonstone

Orthoclase Feldspar (formula: (K,Na)AlSi3O8)

Chrysocolla (with Quartz and Azurite)

Hydrated copper phyllosilicate mineral [Cu2-xAlx(H2-xSi2O5)(OH)4·n(H2O)]

Amethyst

Quartz variety; SiO2 (Silicon Dioxide)

Quartz

Silicon Dioxide (SiO2)

Chert (Arrowhead Fragment)

Microcrystalline Quartz (SiO2)

Chert (Flint nodule)

Silicon dioxide (SiO2)

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Sphalerite in Matrix (Polished Point)

Zinc sulfide (Zn,Fe)S

Rhodochrosite

Manganese Carbonate (MnCO3)

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Chert (Nodule)

Silicon Dioxide (SiO2)

Citrine

Silicon Dioxide (SiO2)

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Pearl

Calcium carbonate (CaCO3) - Aragonite/Calcite variety

Citrine Quartz

Silicon Dioxide (SiO2) with iron impurities

Chrysocolla

Chrysocolla (Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O)

Moonstone

Orthoclase Feldspar ((K,Na)AlSi3O8)

Turquoise

CuAl6(PO4)4(OH)8·4H2O

Amazonite in Pegmatite Matrix with Smoky Quartz

K(AlSi3O8) - Microcline (var. Amazonite) with SiO2 (Quartz)

Petrified Wood

Silicified Wood (primarily SiO2 - Silicon Dioxide)

Liesegang Ring Siltstone

Siltstone with iron oxide Liesegang bands

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Blue Agate (Tumbled and Dyed)

Silicon Dioxide (SiO2) with likely organic dyes

River Stone (likely Mudstone or Siltstone)

Lutite (Clastic sedimentary rock composed of clay and silt-sized particles)

Tiger's Eye

Tiger's eye (Pseudomorph of Quartz after Crocidolite), SiO2

Chert (variations include Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Amethyst

Amethyst (Purple Quartz); formula: SiO2 (Silicon Dioxide)

Quartz (Clear Quartz/Rock Crystal)

Silicon Dioxide (SiO2)

Mookaite Jasper

Silicified radiolarite (SiO2)

Emerald

Beryl (Be3Al2(SiO3)6) with trace Chromium/Vanadium

Sugilite

KNa2(Fe,Mn,Al)2Li3Si12O30 (Potassium Sodium Lithium Iron Manganese Aluminum Silicate)

Bloodstone (Heliotrope)

Cryptocrystalline Quartz (SiO2) with inclusions of Hematite or Chlorite

Amethyst

Silicon Dioxide (SiO2) with iron impurities

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Citrine Quartz

Silicon Dioxide (SiO2)

Tiger's Eye (Unpolished)

Pseudomorph of Quartz after Crocidolite (SiO2)

Mookaite Jasper

Radiolarite (Chert/Jasper variety), formula SiO2

Brecciated Jasper

Silicon Dioxide (SiO2) with iron oxide inclusions