Organic (Often Found By Beachcombers)

Jasper

Silicon dioxide (SiO2)

Amazonite

Microcline (KAlSi3O8) with Trace Elements

Vesicular Basalt (or Porphyritic Scoria)

Vesicular Basalt

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

Sandstone

Clastic sedimentary rock (primarily SiO2)

Riverstone Jasper (Chalcedony)

Silicon Dioxide (SiO2)

Opal

Hydrated amorphous silica (SiO2·nH2O)

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Phyllite

Phyllite (Foliated metamorphic rock)

Sandstone

Arenite (primarily Quartz, SiO2)

Garnet

Garnet Group (Silicate Minerals), formula varies e.g., Almandine Fe3Al2(SiO4)3

Sandstone (Quartzose Pebble)

Clastic Sedimentary Rock (Litharenite/Quartz arenite)

Native Gold Nugget

Native Gold (Au)

Granite

Granite (Felsic Plutonic Rock)

Milky Quartz

Silicon Dioxide (SiO2)

Moqui Marble (Ironstone Concretion)

Iron Oxide Concretion (Fe2O3 / FeO(OH))

Serpentinite

Serpentinite (composed primarily of Serpentine group minerals, Mg3Si2O5(OH)4)

Leopard Skin Jasper

Silicon Dioxide (SiO2) with various inclusions

Mookaite Jasper

Siliceous sedimentary rock (variety of Jasper/Chert)

Amethyst

Silicon Dioxide (SiO2) with traces of Iron and Manganese

Green Aventurine (Propably a tumbled variety)

Aventurine Quartz (SiO2 with inclusions of Fuchsite)

Sandstone (Quartzose)

Arenite (primarily SiO2)

Quartz Pebble

Silicon Dioxide (SiO2)

Sodalite

Sodium Aluminum Silicate Chloride (Na8(Al6Si6O24)Cl2)

Iron Ore / Ironstone Concretion

Mixture of iron oxide/hydroxide minerals, likely some combination of Hematite (Fe2O3), Goethite (α-FeOOH), and Limonite (a general term for hydrated iron oxides of variable composition) or potentially Bauxite (a mixture of aluminum hydroxides, often with iron oxides, (Al(OH)3) and FeO(OH)). The visual characteristics strongly suggest iron-rich material.

Limonite (vibrant yellowish-brown iron oxide)

Limonite (FeO(OH)·nH2O)

Chrysocolla

Hydrated copper silicate (Cu,Al)2H2Si2O5(OH)4·n(H2O)

Rough Sapphire

Corundum (Al2O3)

Banded Calcite (often sold as 'Mexican Onyx')

Calcite (Calcium Carbonate - CaCO3)

Jasper

Silicon dioxide (SiO2)

Chert (Nodule)

Silicon Dioxide (SiO2)

Pietersite

Brecciated Chatoyant Tiger's Eye (SiO2)

Yellow Jade (often Serpentine or Dolomite)

Primarily Serpentine (Mg3Si2O5(OH)4) or Dolomite (CaMg(CO3)2), though the term 'yellow jade' is also sometimes applied to varieties of true nephrite or jadeite.

Sandstone

Arenite

Citrine

Citrine (Silicon Dioxide, SiO2)

Banded Sandstone

Arenite with Liesegang banding

Clear Quartz (Rock Crystal)

Silicon Dioxide (SiO2)

Cullet Glass (Industrial Slag Glass)

Amorphous Silica (SiO2) with metallic oxide impurities

Granite Thin Section

Granitic rock (Phaneritic texture)

Fluorite Octahedron

Fluorite (Calcium Fluoride, CaF2)

Sandstone

Arenite

Chert (variations include Flint or Jasper)

Chert (SiO2)