Not A Natural Rock

Slag Glass

Silicon dioxide with impurities

Faceted Quartz or Cubic Zirconia

SiO2 (Quartz) or ZrO2 (Cubic Zirconia)

Natural Diamond (Faceted)

Diamond (pure carbon crystal, C)

Aura Quartz

Silicon Dioxide (SiO2) with metallic vapor coating

Hag Stone (Holed Quartzite Pebble)

Quartzite (SiO2 based) with natural vug or erosion hole

Magnetite

Fe3O4 (Iron(II,III) oxide)

Polymictic breccia, possibly volcanic breccia

Polymictic clastic breccia; likely a matrix-supported breccia containing lithic fragments, quartz, feldspar, and dark mafic minerals

Argillite (with Barnacles)

Argillite (metamorphosed mudstone/shale)

Green Jasper

Silicon Dioxide (SiO2) with iron and silicate inclusions

Moss Agate

Silicon dioxide (SiO2) with inclusions

Man-made Green Quartz (Lab-grown or Treated)

Silicon Dioxide (SiO2) with artificial coloration

Quartz (Golden Quartz / Citrine / Iron-stained Quartz)

Silicon Dioxide (SiO2)

Smoky Quartz

Silicon Dioxide (SiO2)

Smoky Quartz

Silicon dioxide (SiO2)

Quartz (Smoky Quartz variant)

Silicon Dioxide (SiO2)

Limonite

FeO(OH)·nH2O

Metal Alloy (Likely Pewter or Sterling Silver)

Not a natural geological specimen; composed of refined metals. If pewter, it's a tin-based alloy. If sterling silver, it's 92.5% silver and 7.5% other metals (usually copper).

Demantoid Garnet on Matrix

Demantoid (variety of Andradite Garnet) - Ca3(Fe3+)2(SiO4)3

Engineerged Quartz (Quartz Composite)

SiO2 (Silicon Dioxide) in a polymer resin matrix

Milky quartz

Quartz (silicon dioxide, SiO₂)

Smoky Quartz (with Iron Oxidation)

Silicon Dioxide (SiO2)

Nephrite Jade (Yellow Skin)

Nephrite (Ca2(Mg, Fe)5Si8O22(OH)2)

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurities)

Rutilated quartz crystal

Quartz, silicon dioxide (SiO₂), containing rutile inclusions (TiO₂)

Ruby

Corundum (Al2O3)

Citrine

Quartz (SiO2) - specifically, a variety of macrocrystalline quartz

Man-made Crystal (Lead Glass)

Lead oxide-doped Silica Glass (approx. SiO2 + PbO)

Amber

Succinite (Fossilized Tree Resin) - C10H16O

Coquina

Biogenic Limestone (Calcite, CaCO3)

Dark volcanic pebble, likely basalt

Basalt; fine-grained mafic rock composed mainly of plagioclase, pyroxene, and commonly olivine or magnetite

Sandstone

Quartz Arenite (a common type of sandstone, given the appearance), Arkose, Greywacke (depending on mineralogy)

Amethyst cluster

Amethyst, purple quartz (SiO₂)

Epidote-bearing Rock / Epidote Inclusion

Epidote (Ca2(Al, Fe)3(SiO4)3(OH)) in host rock

Milky Quartz Pebble

Silicon Dioxide (SiO2)

Smoky Quartz

Silicon Dioxide (SiO2)

Smoky Quartz

Silicon Dioxide (SiO2)

Granite pebble

Coarse-grained felsic intrusive igneous rock; mainly quartz, alkali feldspar, plagioclase, and minor biotite or amphibole

Quartz (Herkimer Diamond variant)

Silicon Dioxide (SiO2)

Diamond

C

Diamond (or Diamond Simulant)

Carbon (C)

Diamond (in a gold ring)

Diamond (pure carbon, C)

Chalk

Calcium Carbonate (CaCO3)