Not A Rock (Synthetic Material)

Sandstone with Iron Oxide

Arenite (SiO2 with Fe2O3 inclusions)

Quartz (specifically Milky or Clear Chunk)

Silicon Dioxide (SiO2)

Chrysocolla (with Malachite / Secondary Copper Minerals)

Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O

Quartz–feldspar–mica metamorphic rock, likely gneiss

Gneiss; composition commonly quartz (SiO₂), feldspars, biotite/hornblende, and minor accessory minerals

Quartz-rich translucent pebble, possibly iron-stained quartz or chalcedony

Quartz (SiO₂), potentially microcrystalline quartz (chalcedony)

Biotite granite (weathered granitic rock)

Granite; chiefly quartz (SiO₂), feldspar, and biotite mica

Sandstone (likely Arkosic or Lithic)

Clastic Sedimentary Rock (SiO2 with accessory minerals)

Sandstone (Quartzose type)

Arenite (primarily SiO2)

Milky quartz-bearing rock, possibly quartzite

Quartz (SiO₂), likely in a quartzite or quartz-rich metamorphic matrix

Serpentinized ultramafic rock with magnesite

Serpentinite, chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with likely magnesite (MgCO₃) and minor chromite/magnetite

Chert

Microcrystalline Quartz (SiO2)

Dark volcanic sand / basaltic sand

Basalt-derived lithic sand, chiefly plagioclase, pyroxene, and volcanic glass

Sandstone (Ferruginous)

Ferruginous Sandstone (SiO2 with Fe2O3)

Fossilized bivalve shell

Bivalvia indeterminate; likely a fossil cockle or clam shell, aragonite/calcite replaced or preserved

Light-colored limestone (probable fossiliferous or micritic limestone)

Calcite-rich carbonate rock; predominantly CaCO₃ (calcite)

Chert (often called Flint or Jasper depending on color)

Chert (SiO2 - Microcrystalline or Cryptocrystalline Quartz)

Petrified Wood

Silicified Wood (SiO2)

Quartzite

Quartzite (SiO2)

Quartzite

Metamorphosed Quartz Sandstone

Vesicular basalt (possibly amygdaloidal basalt)

Basalt, chiefly plagioclase feldspar and pyroxene, with possible olivine and secondary mineral infillings

White calcite (likely tumbled calcite or marble fragment)

Calcite, calcium carbonate (CaCO₃); if the specimen is granular and rock-like, it may be marble, a calcite-rich metamorphic rock

Dendritic Agate (Tree Agate)

Chalcedony (Silicon Dioxide, SiO2) with Manganese or Iron Oxide inclusions

Weathered basalt pebble

Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine

Chert (Iron-rich or Jasperoid)

Cryptocrystalline Quartz (SiO2)

Polished jasper pebble

Jasper, microcrystalline quartz (SiO₂) with iron-oxide and clay-mineral impurities

Red Sandstone

Clastic sedimentary rock (primarily SiO2 with Fe2O3)

Flint Pebble

Silicon dioxide (microcrystalline quartz / chalcedony)

Limestone

Calcium Carbonate (CaCO3)

Pumice

Pumice (Volcanic Rock / Glass Froth)

Green serpentine

Serpentine-group minerals, chiefly lizardite and antigorite; approximate formula Mg₃Si₂O₅(OH)₄

Diorite

Intrusive Igneous Rock (Intermediate Composition)

Granite (Pink/Potassium Feldspar Granite)

Felsic Plutonic Rock (Potassium Feldspar, Quartz, Mica, and Amphibole)

Petrified Wood

Silicified Wood (SiO2)

Petrified Wood

Silicified Wood (SiO2)

Amethyst quartz crystal

Quartz, silicon dioxide (SiO₂), purple variety amethyst

Coquina or Fossilized Shell Fragment

Calcium Carbonate (CaCO3) / Biogenic Limestone

Red Chert (Jasper)

Silicon Dioxide (SiO2)

Iron-stained garnet-bearing rock, possibly almandine garnet

Garnet-group silicate, likely almandine (Fe₃Al₂Si₃O₁₂), in a quartz–iron-oxide matrix

Chert (Flint)

Microcrystalline Quartz (SiO2)

Seashell Fossil

Invertebrate fossil (phylum Mollusca)

Polished ocean jasper / brecciated jasper

Jasper, microcrystalline quartz (SiO₂), with iron-oxide and other silicate inclusions

Jasper

Silicon dioxide (SiO2)