Not A Natural Rock

Citrine

Quartz (SiO2) - variety Citrine

Pale green tumbled mineral fragment, likely serpentine or green calcite

Probable serpentine-group mineral (Mg3Si2O5(OH)4) or, less likely, calcite (CaCO3); identification is uncertain from the photograph

Citrine Quartz

Silicon Dioxide (SiO2) with iron impurities

Quartz (likely tumbled or naturally water-worn)

Quartz (SiO₂ - Silicon Dioxide)

Not a geological specimen

N/A (man-made object)

Prasiolite and Quartz Crystal Cluster

Quartz (SiO2); Prasiolite is a variety of Quartz

Kidney Stone

Calculus (Calcium oxalate/Calcium phosphate)

Small seashell fossil or shell fragment

Likely calcium-carbonate shell material, chiefly aragonite or calcite; exact species indeterminate

Yellow Ochre (Limonite)

Limonite (FeO(OH)wH2O)

Pink Quartzite

Metamorphosed Quartz Arenite (SiO2)

Black Onyx

Silicon Dioxide (SiO2)

Turquoise

Hydrous phosphate of copper and aluminium (CuAl6(PO4)4(OH)8·4H2O)

Cherry Quartz with Rose Quartz

Crystalline Quartz (SiO2) with glass-based synthetic components

Opalite

Synthetic Glass / Man-made Opal Simulant

Tumbled Citrine

Silicon Dioxide (Quartz variety)

Citrine (tumbled)

Silicon dioxide, SiO2

Diamond

C

Cat's Eye Moonstone (Simulated/Synthetic or natural Cat's Eye Quartz/Glass)

There is no single scientific name. The appearance suggests either: Moonstone (feldspar group), Cat's Eye Quartz (SiO2), Apatite (Ca5(PO4)3(F,Cl,OH)), or most likely a synthetic material such as Fiber Optic Glass or 'Opalite' (a type of glass).

Smoky Quartz

Silicon Dioxide (SiO2)

Citrine

Silicon Dioxide (SiO2) with ferric iron impurities

Hag Stone

Flint / Chert / Limestone concretion with a natural hole

Polished/tumbled septarian nodule (likely)

Calcite–aragonite–barite septarian concretion; composition varies, commonly calcite (CaCO₃) with clay/mudstone and iron oxides

Red Coral (Precious Coral)

Corallium rubrum (Calcium Carbonate, CaCO3)

Sandstone

Quartz Arenite (a type of sandstone composed of more than 90% quartz)

Turquoise and Red Coral

Turquoise: CuAl6(PO4)4(OH)8·4H2O; Red Coral: Corallium rubrum (organic gemstone)

Opalite

Synthetic glass / Opalized glass

Sandstone (Pebble)

Arenite (primarily SiO2)

Cubic Zirconia (or possibly Diamond)

Zirconium dioxide (or Carbon)

Agate (Dyed) or composite stone

SiO2

Cubic Zirconia

Zirconium dioxide (ZrO2)

Sandstone

Sandstone (lithified arenite/wacke)

Black Obsidian

Obsidian, volcanic glass (Amorphous SiO₂)

Quartz pebble

Silicon dioxide (SiO2)

Quartz Pebble

Silicon Dioxide (SiO2)

Hematite Pebble

Hematite (Fe2O3)

Chert / Flint

Microcrystalline Quartz (SiO2)

Chalcedony (Agate nodule fragment)

Silicon Dioxide (SiO2)

Red Jasper Pebble

Silicon Dioxide (SiO2) with Iron Oxide inclusions

Banded Jasper

Silicon Dioxide with Iron Oxide Inclusions (SiO2)

Quartzite (with Mica / Quartzite Schist)

SiO2 (Silica) with minor Muscovite Mica KAl2(AlSi3O10)(OH)2

Quartz pebble

Silicon dioxide (SiO2)

Quartz Pebble

Silicon Dioxide (SiO2)