Granite

Chert (Common Opal variant)

Microcrystalline Quartz (SiO2)

Vesicular Basalt

Mafic Volcanic Rock (Basalt)

Quartz Pebble

Silicon Dioxide (SiO2)

Golden Healer Quartz

Silicon Dioxide (SiO2) with iron oxide inclusions

Citrine

Citrine (Silicon Dioxide, SiO2)

Peridot (Olivine)

Olivine, (Mg, Fe)2SiO4

Chrysoprase

Nickel-bearing Chalcedony (SiO2 with Ni impurities)

Sandstone (likely Arkosic or Quartzose)

Sandstone (SiO2 dominated)

Clear Quartz

Silicon Dioxide (SiO2)

Sandstone

Arenite (primarily SiO2)

Clear Quartz

Silicon Dioxide (SiO2)

Carnelian Agate

Chalcedony (SiO2) with iron oxide inclusions

Sandstone Cobble

Clastic Sedimentary (Sandstone)

Pyrite (Fool's Gold)

Iron Disulfide (FeS2)

Quartz (Clear Quartz/Rock Crystal)

Silicon Dioxide (SiO2)

Amber

Succinates (Organic Fossilized Resin)

Black Obsidian

Volcanic Glass (Amorphous Silicon Dioxide, SiO2)

Chert / Greenstone

Silicon Dioxide (SiO2) with impurities

Emerald In Matrix

Beryl (Be3Al2Si6O18) with Chromium/Vanadium impurities

Limestone (specifically a Crushed Aggregate fragment)

Calcium Carbonate (CaCO3)

Arsenopyrite in Quartz/Host Rock

Arsenopyrite (FeAsS)

Green Quartzite

Metamorphic Quartz (SiO2) with Chromium-rich inclusions (Fuchsite)

Milky Quartz

Silicon Dioxide (SiO2)

Peridot

Olivine ((Mg, Fe)2SiO4)

Pearl

Organic Mineraloid (CaCO3 + Conchiolin)

Basalt River Stones

Aphantic Mafic Igneous Rock (Basalt)

Clear Quartz

Silicon Dioxide (SiO2)

Red Tiger's Eye

Silicified Crocidolite (Quartz pseudo-morph after Crocidolite), SiO2

Quartzite (River Cobble)

SiO2 (Quartz-rich Metamorphic Rock)

Green Aventurine

Silicon Dioxide (SiO2) with Fuchsite inclusions

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Quartz (Clear Quartz/Rock Crystal)

Silicon Dioxide (SiO2)

Amethyst (Tumbled)

Silicon Dioxide (SiO2 with iron impurities)

Pyrite in Matrix (likely Quartz or Schist matrix)

Iron Sulfide (FeS2)

Clear Quartz Crystal

Silicon Dioxide (SiO2)

Transit Token (RTD Denver)

Nickel-plated brass or bronze alloy (Cu-Sn-Zn-Ni)

Ferruginous Sandstone

Arenite with Iron-Oxide Cement (SiO2 with Fe2O3/FeO(OH))

Chert (Nodule)

Microcrystalline quartz (SiO2)

Basalt River Cobble

Basalt (Mafic Igneous Rock)

Clear Quartz

Silicon Dioxide (SiO2)

Quartz (Citrine variety)

Silicon Dioxide (SiO2)

Herkimer Diamond

Double-terminated Quartz (Silicon Dioxide, SiO2)