Rock

Carnelian Agate Nodule

Silicon Dioxide (SiO2) - Carnelian Chalcedony

Blue Dyed Agate

Silicon Dioxide (SiO2) with artificial pigment

Green Aventurine

Silicon Dioxide (SiO2) with Fuchsite inclusions

Chert (often called Flint)

Chert (Microcrystalline or cryptocrystalline Silica, SiO2)

Banded Agate

Agate (Cryptocrystalline Quartz, SiO2)

Jasper with Agate Inclusions

Jasper (Silicon Dioxide, SiO2) with Chalcedony/Agate

Sandstone

Arenite (composed primarily of SiO2)

Dyed Agate

Silicon Dioxide (SiO2) - variety Chalcedony

Aragonite / Calcite Geode

Calcium Carbonate (CaCO3)

Quartz Geode

Silicon Dioxide (SiO2) in a Secondary Formation

Marble (White)

Metamorphosed Limestone (mainly CaCO3)

Basalt

Basalt (composition predominately plagioclase feldspar and pyroxene)

Quartz Crystal

Silicon Dioxide (SiO2)

Howlite and Purple Amethyst Druzy

Calcium Borosilicate Hydroxide (Howlite) and Silicon Dioxide (Quartz/Amethyst)

Limonite Concretion

Limonite (Hydrated Iron Oxide) FeO(OH)·nH2O

Amethyst (Tumbled)

Quartz (Silicon Dioxide, SiO2) with iron impurities

Sandstone (Micaceous)

Arenite (composed primarily of SiO2)

Milky Quartz Pebble

Quartz (Silicon Dioxide, SiO2)

Turquoise in Matrix

CuAl6(PO4)4(OH)8·4H2O (Hydrous phosphate of copper and aluminium)

Gneiss

Gneiss (High-grade metamorphic rock)

Chert / Flint

Microcrystalline Quartz (SiO2)

Limonitic Iron Ore / Goethite

Hydrated Iron(III) oxide-hydroxide (primarily FeO(OH)·nH2O)

Quartzite

Quartzite (SiO2)

Petrified Wood

Silicified Wood (primarily SiO2)

Porphyry (specifically Porphyritic Basalt or Andesite)

Porphyritic extrusive igneous rock (Mg,Fe)2SiO4 (Olivine inclusions/Plagioclase Feldspar)

Coquina

Biogenic Limestone (Calcium Carbonate - CaCO3)

Turquoise (Green variety)

Hydrous phosphate of copper and aluminum, CuAl6(PO4)4(OH)8·4H2O

Slate

Slate (Metamorphosed Mudstone/Shale)

Quartz-veined Schist (or Metasandstone)

Metamorphic Rock with Quartz Veining (SiO2)

Quartzite

Quartzite (primarily SiO2)

Amethyst

Silicon Dioxide (SiO2) with Fe3+ impurities

Fire Opal (in Matrix)

Hydrated Silica (SiO2·nH2O)

Milky Quartz with Iron Staining

Silicon Dioxide (SiO2)

Carnelian Agate

Silicon Dioxide (SiO2) with Iron Oxide impurities

Milky Quartz (or Iron-Stained Quartz)

Quartz (Silicon Dioxide, SiO2)

Sandstone

Clastic sedimentary rock (primarily SiO2)

Quartz (River Pebble)

Silicon Dioxide (SiO2)

Amygdaloidal Basalt

Amygdaloidal Basalt (Mafic Extrusive volcanic rock)

Peridotite (Olivine)

Peridotite (comprising (Mg,Fe)2SiO4)

Fossil Coral (Honeycomb Coral)

Favosites (extinct genus of Tabulate coral)

Chert (specifically Flint or Gray Chalcedony)

Microcrystalline Quartz (SiO2)

Azurite and Malachite on Matrix

Azurite: Cu3(CO3)2(OH)2; Malachite: Cu2CO3(OH)2