Rock (Likely Sedimentary)

Sandstone

Arenite (SiO2 based)

Weathered sandstone

Quartz-rich sandstone (clastic sedimentary rock)

Alluvial stream gravel (mixed rock specimens)

Polymictic fluvial deposit; likely mixtures of quartzite, sandstone, shale, chert, basalt, and granite-derived minerals

Geode with Quartz and possibly Jasper/Hematite

Quartz (SiO2) and Chalcedony (cryptocrystalline SiO2), possibly stained by iron oxides

Fossiliferous limestone

Bioclastic limestone, likely containing brachiopod or bivalve impressions

Mixed rounded river pebbles

Polymictic alluvial gravel; likely quartz/quartzite, chert, and weathered feldspathic rocks

Tumbled reddish-brown pebble

Indeterminate lithic fragment; possibly iron-stained quartzite, chert, or jasper

Polished red jasper and carnelian specimens

Jasper: microcrystalline quartz (SiO₂) colored by iron oxides; carnelian: orange-red chalcedony, also SiO₂

Pyrite (on Shale/Matrix)

Iron Disulfide (FeS2)

Water-worn Pebble

Unidentified Rock Type (Likely Basalt or Graywacke)

Foliated Metamorphic Rock (likely Gneiss or Schist)

Gneissic Metamorphic Rock

Likely weathered limestone or calcitic marble

Calcite (CaCO₃), probably micritic limestone; marble is a possible metamorphic alternative

Chert (or Chalcedony) Nodule

Microcrystalline Quartz (SiO2)

Fossiliferous Limestone

Biogenic Limestone (Calcium Carbonate, CaCO3)

Chert Pebble

Microcrystalline or cryptocrystalline Quartz (SiO2)

Sandstone (Water-worn Cobble)

Arenite (variable composition, primarily SiO2)

Dark metamorphic rock, likely schist or phyllite

Quartz–mica schist/phyllite; chiefly quartz, mica, and feldspar

Iron-rich rock, possibly weathered basalt or ironstone

Tentatively ferruginous basalt; exact identification requires testing

Weathered iron-rich rock, possibly ironstone or altered basalt

Indeterminate; likely ferruginous basalt/ironstone containing hematite-goethite and silicate minerals

Weathered limestone

Limestone, predominantly calcite (CaCO₃)

Weathered brown stone, likely sandstone or mudstone

Indeterminate clastic sedimentary rock; likely quartz-rich sandstone or lithified mudstone

Weathered granite or granitic rock

Granite; primarily quartz, feldspar, and mica

Gneiss, likely migmatitic or granitic gneiss

Banded quartz–feldspar–mica gneiss; composition chiefly quartz, alkali/plagioclase feldspar, biotite and accessory minerals

Weathered quartz-rich metamorphic rock, likely gneiss or quartzite

Quartz (SiO₂)-bearing gneiss; exact identification requires a fresh surface and tests

Brecciated jasper

Chalcedony–quartz aggregate, predominantly SiO₂, with iron-oxide coloring

Rounded quartz-rich cobble, likely quartzite

Quartzite; predominantly SiO₂ (recrystallized quartz)

Polished fossiliferous limestone

Bioclastic limestone, commonly called fossil limestone or marble-like limestone

Chert (often called Jasper or River Siltstone)

Microcrystalline Quartz (SiO2)

Chert (often called Jasper or River Siltstone)

Microcrystalline Quartz (SiO2)

Quartz-rich geode or mineralized cavity in host rock

Likely a quartz-bearing geode; the pale crystals may be quartz (SiO₂), but the photo is not detailed enough for a firm identification.

Sandstone (Quartz-rich)

Arenite (composed primarily of SiO2)

Small iron-oxide-rich rock fragment (possibly ferruginous sandstone)

Ferruginous sandstone or ironstone; likely quartz grains cemented by iron oxides such as hematite/goethite

Mixed stream gravel and cobbles

Polylithic alluvial deposit; individual clasts are not identifiable at this resolution

Weathered feldspathic sandstone

Quartz–feldspar arenite, likely arkose

Weathered quartz-rich rock, possibly quartzite or iron-stained quartz

Quartzite (mostly SiO₂), with possible iron-oxide staining and minor feldspar/mica

Dark river pebble (likely basalt or andesite)

Fine-grained mafic/intermediate volcanic rock; commonly basalt (plagioclase ± pyroxene/olivine)

Quartz geode

Quartz (SiO₂), likely in a chalcedony or other silica-rich host rind

Banded gneiss

Quartzo-feldspathic gneiss, likely biotite-bearing

Weathered quartz-rich rock, likely sandstone or quartzite

Quartz sandstone (possibly weakly metamorphosed quartzite); predominantly SiO₂

Banded metamorphic rock, likely gneiss or migmatitic gneiss

Quartz–feldspar–mica gneiss; exact identification requires a fresh surface and mineral tests

Sandstone (likely Arkosic or Lithic Sandstone)

Sandstone (SiO2 predominant)

Smooth river pebble, likely quartz-rich sandstone or quartzite

Probable quartz arenite (sandstone) or quartzite; mainly SiO₂ with minor iron-bearing minerals