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

Limonite (Iron Stone)

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

Granite with Epidote

Granite, containing quartz, feldspar, and epidote

Milky Quartz Pebble

Quartz (Silicon Dioxide, SiO2)

Diorite (River Rock)

Intermediate plutonic igneous rock

Chert (Field-collected Arrowhead-shaped Fragment)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Copper-bearing Quartz (with Malachite and Iron Oxides)

Quartz (SiO2) with Malachite (Cu2CO3(OH)2) and Hematite/Limonite (Fe2O3)

Granite Pegmatite

Phaneritic Felsic Igneous Rock (Granite)

Chert (Jasper/Chalcedony variety)

Microcrystalline Quartz (SiO2)

Quartzite with Iron Mineral Banding

Silicon Dioxide (SiO2) with Ferric Oxide (Fe2O3) staining

Chert Nodule (with Flint core)

Sedimentary Cryptocrystalline Quartz (SiO2)

Quartz Pebble

Silicon Dioxide (SiO2)

Limestone

Calcium Carbonate (CaCO3)

Quartz Pebble

Silicon Dioxide (SiO2)

Petrified Wood

Silicified Wood (SiO2)

Geode (unopened)

Calcedony-lined Geode (SiO2)

Banded Chert / Flint

Silicon dioxide (SiO2)

Granodiorite (Gneissic Pebble)

Granodiorite displaying minor foliation

Shale

Fissile Mudstone (primarily composed of phyllosilicate minerals like kaolinite, montmorillonite, and illite)

Chert (Jasper variety)

Microcrystalline Quartz (SiO2)

Pink Tumbled Agate (Dyed)

Silicon Dioxide (SiO2) with artificial dyes

Amethyst (Rose de France varieties or Amethystine Quartz)

Silicon Dioxide (SiO2) with iron impurities

Arsenopyrite in Quartz/Host Rock

Arsenopyrite (FeAsS)

Limonite after Pyrite (Prophecy Stone)

Limonite (FeO(OH)·nH2O) replacing Pyrite (FeS2)

Limestone

Limestone (Calcium Carbonate: CaCO3)

Clear Quartz

Silicon Dioxide (SiO2)

Quartz (Citrine or Iron-Stained variety)

Silicon Dioxide (SiO2)

Bituminous Coal (with Anthracite or Vitrinite inclusion)

Organic-rich Sedimentary Rock (Carboniferous classification)

Limestone

Calcium Carbonate (CaCO3)

Heat-Treated Amethyst (Commercial Citrine)

Silicon Dioxide (SiO2) - Macro-crystalline Quartz

White Quartz Pebble

Quartz (Silicon Dioxide, SiO2)

Chert (Jasper nodule)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Gold Ore in Quartz

Native Gold (Au) in Quartz (SiO2)

Clear Quartz

Silicon Dioxide (SiO2)

Diorite (River Cobble)

Intermediate plutonic igneous rock

Jasper

Silicon dioxide (SiO2)

Chert (Iron-stained)

Microcrystalline quartz (SiO2)

Quartz on Sandstone

Silicon Dioxide (SiO2) in Lithic Sandstone

Quartzite River Rock (with Limonite staining)

Quartzite (SiO2)

Ferruginous Quartz

Silicon Dioxide (SiO2) with Limonite/Hematite inclusions

Quartz

Silicon Dioxide (SiO2)

Yellow Quartz (Citrine/Yellow Chalcedony)

Silicon Dioxide (SiO2)

Citrine

Crystalline Quartz (SiO2) with iron impurities