Sedimentary Or Metamorphic

Dark gray rounded river pebble

Likely basalt or fine-grained volcanic rock; exact identification requires testing

Natural freshwater pearls

Pearl (nacreous calcium carbonate; chiefly aragonite, CaCO₃)

Weathered dark stone, possibly basalt

Basalt; commonly plagioclase feldspar, pyroxene, and minor olivine

Painted River Rock

Artificially Coated Sedimentary Rock

Rounded gray river cobble

Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests

Mixed collection of common river stones

Varied lithologies, visibly including quartz-rich rock, dark mafic rock, sandstone, and purple quartz-bearing material

Sandstone with Liesegang Rings

Quartzose Sandstone with Iron Oxide Precipitation

Painted River Rock

Painted Quartzite or Smooth Siltstone

Mixed river stones and gravel

Polymictic alluvial clasts; individual pieces may include quartzite, granite, basalt, sandstone, limestone, and slate

Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Fossilized bone fragment (probable mammalian tooth or bone)

Mineralized bone, commonly hydroxyapatite [Ca5(PO4)3(OH)] replaced or impregnated by silica/calcite

Baked-clay ceramic fragment (likely brick or pottery)

Fired clay, primarily aluminosilicate minerals; not a natural rock

Quartzite Chert Pebble

Sedimentary Chert / Metamorphic Quartzite (SiO2)

Likely quartz-rich metamorphic rock (quartzite or quartz-veined schist)

Quartzite/siliceous schist; chiefly quartz (SiO₂), with probable mica and iron-oxide staining

Greenschist

Greenschist (composed mainly of chlorite, epidote, actinolite, and albite)

K2 Stone

Azurite in Granite

Quartz-rich river pebble, likely milky quartz

Milky quartz (SiO₂), possibly a quartzite or quartz-rich silicate pebble

Beach Pebble (Quartzite / Sandstone)

Quartz-rich sedimentary or metamorphic rock pebble

Anthracite Coal

Anthracite (Carbon-rich Sedimentary-to-Metamorphic Rock)

Small white mineral fragment

Likely quartz (SiO₂), possibly calcite (CaCO₃)

Milky Quartz with Iron Inclusions

Quartz (Silicon Dioxide, SiO2)

Anthracite Coal

Anthracite (Carbon-based sedimentary-derived metamorphic rock)

Quartz-rich limestone or calcitic marble

Calcite (CaCO₃), possibly with quartz (SiO₂)

Weathered fine-grained stone, likely sandstone or quartzite

Quartz-rich sandstone (possibly weakly metamorphosed quartzite); predominantly SiO₂

Rounded gray stone, likely slate or fine-grained sandstone

Probable slate (low-grade metamorphosed shale) or lithic sandstone; exact identification requires testing

Oyster shell fragment

Ostreidae shell; primarily calcite (CaCO₃)

Brown quartz-rich pebble (likely chert or weathered quartzite)

Quartz (SiO₂), possibly microcrystalline quartz/chert or quartzite

Pyrite-bearing rock (likely pyrite schist or pyritized shale)

Pyrite (FeS₂) in a fine-grained schistose or shale matrix

Jasper Conglomerate (Puddingstone)

Siliceous Conglomerate (Quartz and Jasper clasts in a fine-grained matrix)

Possible shale or slate fragment

Fine-grained clay-rich rock; possibly slate (low-grade metamorphosed shale)

Green Jasper

Silicon Dioxide (SiO2) with iron silicate inclusions

River Pebbles and Quartz

Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

Polished Stone Pendant (Identity Unclear)

Unknown (Possibly Jasper/Agate/Quartz mixture)

Calcite

Calcite (CaCO3)

Tiger's Eye

Quartz pseudomorph after crocidolite (SiO2)

White Buffalo Turquoise (or Howlite/Magnesite)

Calcite/Dolomite or Magnesite with Chert/Quartz inclusions

Limonite pseudomorph after pyrite

Goethite / Limonite pseudomorph after Pyrite (Fe3+O(OH) replacing FeS2)

Orange Calcite (likely polished specimen)

Calcite

Agate

SiO2 (Chalcedony/Quartz)

Agate

Silicon Dioxide (Chalcedony), SiO2

Gravel / Small Pebble

Rock Fragment (Gravel)

Agate

Chalcedony (SiO2)