The Purple Specimen Is A Mineral (Amethyst); The White Specimen Is A Sedimentary Rock (Limestone Or Marble).

Snowflake Obsidian

Spherulitic Volcanic Glass (primarily SiO2 with Cristobalite inclusions)

Prasiolite

Silicon Dioxide (SiO2) with iron impurities

Green Calcite

Calcite (CaCO3)

Sandstone (Greywacke)

Arenite / Clastic Sedimentary Rock

Chert Nodule in Limestone

Chert (Microcrystalline Quartz, SiO2) and Limestone (Calcium Carbonate, CaCO3)

Lapis Lazuli

Complex mixture containing Lazurite ((Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2), Calcite, and Pyrite

Chert Nodule

Chert (SiO2)

Amethyst

Quartz (Silicon Dioxide with Iron impurities), SiO2

Sandstone

Arenite (SiO2 based)

Dendritic Opal

Opalized Chalcedony with Manganese Inclusions (SiO2 · nH2O)

Quartz / Calcite Vein Rock

Silicon Dioxide (SiO2) or Calcium Carbonate (CaCO3)

Limonite (after Pyrite Pseudomorph)

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

Banded Jasper

Silicon Dioxide (SiO2) with iron oxide inclusions

Amethyst (Chevron/Banded Amethyst)

Silicon Dioxide (SiO2) with iron impurities

Chert (Pink Jasper)

Microcrystalline Quartz (SiO2)

Chert (Fossiliferous)

Silicon dioxide (SiO2)

Marble (Fire and Ice or Pink Veined)

Metamorphosed Limestone (principally CaCO3)

Sandstone (Micaceous)

Arenite (composed primarily of SiO2)

Quartzite

Quartzite (SiO2)

Sandstone (with Iron Staining)

Clastic sedimentary rock (primarily SiO2 with Fe2O3 oxides)

Sandstone (Water-worn Pebble)

Clastic Sedimentary Rock (primarily SiO2)

Sandstone concretion (Ironstone-stained)

Arenite with Limonite/Hematite staining (Silica-based with Iron Oxides)

Sandstone (with Limonite staining)

Arenite (primarily SiO2 with FeO(OH)·nH2O)

Green Calcite

Calcium Carbonate (CaCO3)

Cryptocrystalline Quartz (Agate/Chert)

Silicon dioxide (SiO2)

Chert (often called Flint or River Pebble)

Microcrystalline Quartz (SiO2)

Sandstone (Ferruginous)

Arenite (with iron oxide cement, Fe2O3)

Quartz Druzy Geode Fragment

Silicon Dioxide (SiO2)

Chert (Commonly known as Flint or Jasper when pigmented)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Lapis Lazuli

Lapis Lazuli (Complex silicate mixture)

Chalcedony with inclusions (Agate/Quartz)

Silicon Dioxide (SiO2)

Orca Agate (Blue Chalcedony)

Silicon Dioxide (SiO2)

Chalcedony (Agate)

Silicon Dioxide (SiO2)

Chert (Black Chert)

Microcrystalline Silica (SiO2)

Chert (often called Flint when dark)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Sandstone (specifically Banded Sandstone)

Clastic sedimentary rock (primarily SiO2)

Sandstone (Ferruginous)

Ferruginous Sandstone (SiO2 with Fe2O3/FeO(OH) cement)

Marble

Recrystallized Calcite (CaCO3)

Amethyst

Amethyst (Silicon Dioxide, SiO2)

Chert (with Limestone matrix)

Silicon dioxide (SiO2)

Chert (Chert Nodule)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Citrine

SiO2 (Silicon Dioxide)