Rock (Likely Sedimentary)

Weathered granite fragment

Granite, chiefly quartz, potassium feldspar, plagioclase, and biotite/hornblende

Weathered sandstone pebble

Quartz-rich sandstone, likely ferruginous litharenite

Chert (Jasper/Agate variety)

Cryptocrystalline Quartz (SiO2)

Conglomerate

Conglomeratic Sandstone

Weathered rock pebble, possibly sandstone

Likely quartz-rich sandstone; precise identification requires closer examination

Rounded dark river pebble

Likely basalt or a basaltic volcanic rock; exact identification requires a fresh surface and tests

Weathered limestone (likely fossiliferous limestone)

Calcite-rich carbonate rock, predominantly CaCO₃

Gray River Pebble (likely Limestone or Siltstone)

Sedimentary Rock (Calcium Carbonate or Siliciclastic)

Rounded pebble (likely quartz-rich sandstone or weathered chert)

Indeterminate from image; possibly quartz (SiO₂)-rich lithic material

Yellow Chalcedony (likely Carnelian or Agate)

Silicon dioxide (SiO2)

Chert (Jasper/Agate mix)

Microcrystalline Quartz (SiO2)

Sandstone (likely Ferruginous)

Arenite (SiO2 based with Fe2O3/FeO(OH) cement)

Tumbled gneiss (likely biotite gneiss)

Gneiss; quartz–feldspar–biotite assemblage

Porphyritic Andesite/Basalt or Diorite River Rock

Porphyritic Igneous Rock

Coarse-grained metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss (probable; exact identification requires a fresh surface and tests)

Possible weathered sandstone or iron-rich sedimentary rock

Indeterminate; likely quartz-rich sandstone with iron-oxide cement

Veined Pebble (likely a Quartz-Veined Pebble)

Pebble with Mineral Vein (e.g., Quartz Vein in a Chert/Mudstone Pebble)

Rounded river or beach pebble

Likely quartz-rich sandstone or quartzite; exact identification requires a close-grained view and hardness test

Painted River Rock

Polished fluvial clast with acrylic/synthetic pigment coating

Rounded sandstone pebble

Quartz-rich sandstone (likely arkosic or lithic sandstone)

Brown chert or silicified limestone fragment

Microcrystalline quartz (SiO₂), possibly occurring as chert; exact identification requires testing

Limestone with Calcite Crust

Sedimentary Calcium Carbonate (CaCO3)

Fossiliferous Limestone with Crinoid stems

Calcite-rich Biogenic Sedimentary Rock (CaCO3)

River Cobble (Quartzite-rich Sandstone)

Clastic Sedimentary Rock (Litharenite/Quartzite transition)

Chert (Iron-rich River Pebble)

Cryptocrystalline Quartz (SiO2)

Sandstone Concretion

Arenaceous concretion (primarily SiO2 with Fe2O3 staining)

Sandstone (likely Quartzose Sandstone)

Arenite (SiO2 principal composition)

Likely blue-gray slate

Slate, a fine-grained metamorphic rock composed mainly of mica-group minerals and quartz

Mica-rich metamorphic rock, likely biotite schist

Biotite–quartz schist; probable composition of quartz, biotite, feldspar, and minor sulfide or iron-oxide minerals

Iron-stained quartz-rich stone (probable jasper or chert)

Microcrystalline quartz (SiO₂), likely ferruginous jasper/chert

Sandstone (Ferruginous)

Arenite (Fe2O3 enriched)

Gneiss (Gneissic Granite)

Gneiss

Weathered granite or granitic gneiss fragment

Quartz–feldspar–mica granite; possibly foliated granitic gneiss

Rounded gray pebble, likely quartz-rich river stone

Probably quartzite or quartz-rich sandstone; exact identification requires testing

Sandstone (Weathered Coastal Boulder)

Arenite (composed primarily of SiO2)

Rounded sandstone pebble

Quartz-rich sandstone, likely arkosic or lithic sandstone

Weathered, iron-stained rock (likely sandstone or breccia)

Indeterminate clastic sedimentary rock; possible ferruginous sandstone or weathered breccia

Pet Rock (Quartzite/Sandstone River Rock)

Silicon Dioxide (SiO2) mixture

Pebble (likely a type of sandstone or quartzite pebble)

Clastic Sediment (specifically, a rudite-sized clast). If the pebble is composed of a specific rock type, its scientific name would be that rock type (e.g., 'Quartzite pebble', 'Granite pebble', 'Chert pebble'). Given its appearance, it is likely a metamorphic quartzite pebble or a hard sandstone pebble.

Sandstone with Secondary Mineral Encrustation

Arenite with Silica/Calcite deposits (SiO2 or CaCO3)

Sandstone (likely Quartzose Sandstone)

Arenite (SiO2 predominantly)

River Cobbles (Quartzite and Sandstone)

Metamorphosed Quartz-rich Sedimentary Rock