Biogenic Material

Granite

Granite

Chert Pebble

Microcrystalline Quartz (SiO2)

Flint / Chert

Silicon dioxide (SiO2)

Flint Pebble

Sedimentary cryptocrystalline quartz (SiO2)

Micrometeorite (Spherule)

Extraterrestrial Accretion Spherule

Iron-stained quartz-rich rock, possibly weathered granite or pegmatite

Quartz–feldspar rock with iron-oxide alteration; exact identification is uncertain from the photograph

Likely bituminous coal or carbon-rich shale fragment

Bituminous coal; predominantly carbon with macerals and minor clay/pyrite

Diamond (or diamond simulant)

C

Tiger’s-eye

Chatoyant quartz (SiO₂), typically pseudomorphous quartz after crocidolite

Orbicular rhyolite (orbicular jasper-like volcanic rock)

Silica-rich rhyolite containing concentric feldspar–quartz orbicules, commonly with iron-oxide staining

Banded metamorphic rock, likely gneiss or amphibolite

Composition uncertain; probable quartz–feldspar–amphibole assemblage

Tumbled yellow quartz (likely citrine or iron-stained quartz)

Quartz, SiO₂; yellow color from trace iron or irradiation/heat-related coloration

Green aventurine (probable)

Quartzite dominated by quartz (SiO₂), with green fuchsite mica inclusions

Tumbled quartz-rich pebble

Likely milky quartz with a dark mafic inclusion or attached basalt; exact identification requires testing

Petrified Wood (Silicified Fossil)

Silicified Wood (SiO2)

Tumbled quartz-rich pebble, likely jasper or chert

Microcrystalline quartz (SiO₂), possibly iron-stained jasper

Fossil scallop shell

Bivalve mollusk shell, likely family Pectinidae; primarily calcite (CaCO₃)

Rounded quartz-rich pebble

Lithic pebble; likely quartz/quartzite with iron-oxide staining

Rounded brown pebble, likely weathered basalt or iron-rich chert

Indeterminate; possibly basalt (fine-grained mafic silicate rock) or ferruginous chert

Mudstone

Argillite / Siliciclastic sedimentary rock

Serpentine

Serpentine group ((Mg,Fe,Ni,Al,Zn,Mn)3(Si,Al)2O5(OH)4)

Tumbled brown pebble

Indeterminate; likely quartz-rich sandstone or chert

Banded gneiss pebble

Biotite–quartz–feldspar gneiss (composition variable)

Petrified wood

Silicified wood, chiefly microcrystalline quartz (SiO₂)

Tumbled jasper or rhyolitic porphyry

Silicic volcanic rock, likely rhyolite (quartz- and feldspar-rich), possibly jasperized

Quartz / Quartzite

Silicon Dioxide (SiO2)

Sandstone

Arenite (primarily SiO2)

Sandstone (Tumbled/River Pebble)

Arenite (composed primarily of SiO2)

Limestone

Calcite (CaCO3)

Dyed blue-purple tumbled stone, likely quartz or calcite

Uncertain; commonly dyed quartzite/chalcedony (SiO₂) or calcite (CaCO₃)

Tumbled greenstone, likely serpentine or altered basalt

Serpentine-group minerals, chiefly Mg₃Si₂O₅(OH)₄; possibly chlorite/epidote-bearing mafic rock

Purple chalcedony or lavender quartz

Cryptocrystalline quartz, SiO₂ (likely chalcedony; identification uncertain from photograph)

Ring with an Orange Inlay

N/A (Man-made object)

Likely sandstone pebble

Quartz-rich sandstone (composition cannot be confirmed from the image)

Tumbled blue-gray stone, likely basalt or slate

Probable fine-grained basalt; exact identification is uncertain from the photograph

Polished dark greenstone with quartz vein

Likely chlorite-rich metabasalt or greenschist with a quartz–feldspar vein

Tumbled green aventurine (probable)

Quartzite dominated by quartz (SiO₂) with fuchsite or other green inclusions

Polished red jasper (likely brecciated jasper)

Microcrystalline quartz/chalcedony, SiO₂, colored mainly by iron oxides

Petrified Wood

Silicified wood (Quartz/Chalcedony replacement of cellulose)

Petrified Wood

Silicified Wood (SiO2)

Tumbled river pebble, likely limestone or weathered chert

Indeterminate carbonate/siliceous pebble; possible micritic limestone or chert

Turquoise bead bracelet

Turquoise — hydrated copper aluminum phosphate, CuAl₆(PO₄)₄(OH)₈·4H₂O