Sedimentary (Chemically Precipitated) Or Metamorphic

Basalt (River Cobble)

Basalt (Mafic volcanic rock)

Quartz Pebble

Quartz (Silicon Dioxide, SiO2)

Gneiss Pebble

Gneiss

Gneiss (specifically a Granitic Gneiss)

Gneiss (typically composed of Quartz, Feldspar, and Mica/Amphiboles)

Petrified Wood

Silicified Wood (primarily Quartz / Chalcedony: SiO2)

Gneiss (specifically Biotite Gneiss)

Gneiss (high-grade metamorphic rock primarily composed of Silicates)

Green Fluorite

Calcium Fluoride (CaF2)

Quartz Pebble

Silicon Dioxide (SiO2)

Sunstone

Aventurine Feldspar (composition: (Ca,Na)((Al,Si)2Si2O8))

Amethyst (Tumbled Chips)

Amethyst (Silicon Dioxide with Iron impurities, SiO2)

Amethyst

Silicon Dioxide (SiO2) with trace Iron (Fe)

Milky Quartz

Quartz (Silicon Dioxide, SiO2)

Chakra Stone (Composite / Man-made Bonded Gemstones)

Composite of Quartz, Lapis Lazuli, Aventurine, Tiger's Eye, and Jasper (SiO2, (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2, etc.)

Clear Quartz Crystal

Quartz (Silicon Dioxide, SiO2)

Clear Quartz (Rock Crystal)

Silicon Dioxide (SiO2)

Blue Calcite

Calcium Carbonate (CaCO3)

Pyrite (Fool's Gold)

Iron Disulfide (FeS2)

Pyrite

Iron Sulfide (FeS2)

Milky Quartz

Quartz (Silicon Dioxide, SiO2)

Clear Quartz Crystal Cluster

Silicon Dioxide (SiO2)

Pyrite on Quartz matrix

Iron Disulfide (FeS2) on Silicon Dioxide (SiO2)

Clear Quartz (Rock Crystal Fragments)

Silicon Dioxide (SiO2)

Gneiss (specifically a granitic gneiss cobble)

Gneiss (high-grade regional metamorphic rock)

Travertine (used in construction, not a 'specimen' in situ)

Travertine

Petrified Wood

Silicified Wood (SiO2)

Quartzite

Quartzite (primarily SiO₂)

Brown Jasper

Jasper (a cryptocrystalline variety of Quartz, SiO2)

Azurite

Azurite (Cu3(CO3)2(OH)2)

Opalite

Synthetic Glass (Hydrated Crystalline Silicon Dioxide simulation)

Red Jasper

Silicon dioxide (SiO2) with Iron Oxide (Fe2O3) inclusions

Red Jasper

Silicon dioxide (SiO2) with iron oxide (Fe2O3) inclusions

Chert Pebble / Brachiopod Fossil Internal Mold

Silicon Dioxide (SiO2) / Fossil: Brachiopoda (generic internal mold)

Copper-bearing Quartz (likely Malachite on Quartz matrix)

Cu2CO3(OH)2 (Malachite) on SiO2 (Quartz)

Amethyst (Rough Quartz)

Silicon Dioxide (SiO2 with Iron impurities)

Chrysocolla in Malachite

Cu2CO3(OH)2 (Malachite) / Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (Chrysocolla)

Anthracite Coal

Anthracite

Aventurine (Green)

Silicon Dioxide (Quartz) with inclusions typically of Fuchsite; SiO2

Jasper

Jasper (Silicon Dioxide, SiO2)

Jasper (Red Jasper)

Silicon Dioxide (SiO2) with Hematite inclusions

Pyrite

Pyrite (Iron sulfide, FeS₂)

Quartz (Milky Quartz)

Silicon Dioxide (SiO2)

Pyrite (on a metal substrate)

Iron Sulfide (FeS2)