Rock (Likely Sedimentary)

Rounded weathered pebble

Likely fine-grained sandstone, siltstone, or weathered volcanic rock; exact identification is uncertain from the image

Iron-stained quartz fragment (probable quartzite or chert)

Quartz, SiO₂; possibly iron-oxide-stained microcrystalline silica

Fossil shell fragment

Likely a fossilized bivalve or brachiopod valve; exact identification requires the other valve, locality, and matrix

Sandstone (River Cobble / Pebble)

Sedimentary Rock (Quartz Sandstone / Arenite)

Weathered sandstone

Quartz-rich clastic sandstone, chiefly SiO₂ with minor feldspar, lithic grains, and iron-oxide/clay cement

Fossil gastropod shell

Fossilized gastropod, likely a small marine snail; exact genus cannot be determined from the image

Siltstone or Mudstone

Argillaceous sedimentary rock

Pumice

Pumice (Amorphous volcanic glass)

Small rounded pebble (rock type indeterminate)

Unidentified lithic pebble; specific composition cannot be determined from the image

Sandstone

Clastic sedimentary rock (primarily SiO2)

River Stone (likely Siltstone or Mudstone)

Argillaceous Sedimentary Rock

Sandstone (with carbonaceous plant fragments)

Arenite (composed primarily of SiO2)

Gray Limestone

Carbonate rock (CaCO3)

Tumbled quartz-rich pebble

Quartz (SiO₂), likely a rounded quartzite or quartz-rich sandstone pebble

Fossilized Shell Fragment

Invertebrate marine fossil, likely calcium carbonate replacement

Sandstone Pebble

Arenite (Sandstone)

Mixed rough mineral specimens, likely quartz-bearing rocks

Probable quartz (SiO₂), with possible feldspar, iron oxides, and altered host rock

Sandstone

Arenite

Quartz geode

Microcrystalline and crystalline quartz, SiO₂, likely with chalcedony and iron-oxide staining

Rounded gray river pebble, likely fine-grained basalt or andesite

Basaltic-andesitic volcanic rock; commonly plagioclase feldspar, pyroxene, and minor iron oxides

Conglomerate

Clastic sedimentary rock (Psephite)

Likely bituminous coal

Coal, predominantly carbon-rich organic matter with variable maceral and mineral content

Unidentifiable embedded dark fragment

Indeterminate; possibly a dark silicate mineral or lithic inclusion

Fossil-bearing fine-grained sedimentary rock

Likely fossiliferous mudstone or shale; visible feature may be a plant fragment, trace fossil, or mineral vein

Conglomerate

Conglomerate (clastic sedimentary rock)

Painted River Rock

Artificially Coated Sedimentary Rock

Weathered porphyritic volcanic rock (likely basaltic andesite)

Porphyritic basaltic andesite; mineral assemblage likely plagioclase, pyroxene, and iron oxides

Small pale stone, likely quartzite or limestone fragment

Indeterminate; possible quartzite (mostly SiO₂) or calcitic limestone (CaCO₃)

Rounded river pebble (lithology unclear)

Indeterminate natural rock; no specific mineral or rock type can be identified from the image

Chert (Yellow/Tan Variety)

Chert (SiO2)

Rough amber-colored quartz or calcite fragment

Likely quartz (SiO₂) or calcite (CaCO₃); exact identification requires testing

Greywacke (likely)

Greywacke (a type of sandstone)

Sandstone (Sedimentary Rock)

Arenite (SiO2 based)

Fossil bivalve or brachiopod in sedimentary rock

Unidentified fossil shell impression; likely a ribbed bivalve or brachiopod preserved in shale/siltstone

Small quartz-rich mineral fragment

Quartz (SiO₂), possibly milky or chalcedonic quartz

Quartz-encrusted Matrix

Silicon Dioxide (SiO2) with Ferruginous Sandstone

Conglomerate

Clastic Sedimentary Rock (Conglomerate)

Sandstone (Ferruginous)

Arenite (primarily SiO2 with Iron Oxide cement)

Rounded gray stone, likely slate or fine-grained sandstone

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

Sandstone

Arenite (SiO2 based)

Weathered yellow-brown rock fragment

Indeterminate; possibly iron-stained sandstone or weathered limestone

Gastropod Fossil (Snail Steinkern)

Class Gastropoda fossil, composed of Calcium Carbonate (CaCO3)