Not A Natural Rock

Scoria

Vesicular Basalt / Scoria

Weathered iron-rich rock, possibly limonite-bearing sandstone

Limonite/goethite mixture, approximately hydrated iron oxides (FeO(OH)·nH₂O), possibly coating sandstone or ironstone

Black Obsidian

Obsidian / Amorphous volcanic glass (SiO2)

Likely weathered granite or granitic pegmatite

Granite; mainly quartz (SiO₂), feldspar, and mica, with possible iron-oxide staining

Asphalt / Bituminous Aggregate

Bituminous mixture (Hydrocarbon-based sediment)

Sandstone (River Cobble)

Sandstone (composed predominantly of SiO2 - Quartz)

Uncertain rounded gray stone

Possibly granite, gneiss, or a glacially transported granitoid

Asphalt

Asphalt concrete

Dyed Agate

Silicon Dioxide (SiO2) with artificial pigment

River Cobble (likely Basalt or Greenstone)

Mafic Igneous Rock (with possible chloritic alteration)

Yellow Quartz Pebble

Silicon Dioxide (SiO2)

Clear Quartz (Tumbled)

Silicon Dioxide (SiO2)

Chert (Green and Black Jasper variant)

Cryptocrystalline Quartz (SiO2)

Sandstone

Sandstone (clastic sedimentary rock)

Clear Quartz (Rock Crystal)

Silicon Dioxide (SiO2)

Beach Pebble (Gray Quartzite / Fine-Grained Metasediment)

Quartzite (SiO2-dominated rock) / Metamorphic Sandstone

Granite

Granite (silica-rich intrusive igneous rock)

Dark fine-grained rock, likely basalt

Basalt; chiefly plagioclase feldspar and pyroxene, commonly with olivine and iron oxides

Sandstone (Micaceous/Feldspathic variant)

Arenite (specifically subarkose or lithic arenite)

Sandstone

Arenite (Sedimentary rock composed of sand-sized grains, primarily SiO2)

Emerald in Host Rock

Beryl (Be3Al2Si6O18) containing Chromium and/or Vanadium

Small pale mineral fragment

Unidentified; possibly quartz, calcite, or feldspar

Basalt Pebble

Basalt

Quartzite

Quartzite (SiO2)

Basalt and weathered granite-like rock

Dark specimen: basalt, likely vesicular or fine-grained mafic volcanic rock; tan specimen: uncertain, possibly weathered granite or iron-stained felsic rock

Tumbled gray stone, likely serpentinite or weathered basalt

Tentatively serpentinite (predominantly serpentine-group minerals); identification is uncertain from the photograph

Jasper

Silicon dioxide (SiO2)

Honey Calcite

Calcite (Calcium Carbonate, CaCO3)

Chalcedony Geode Fragment

Silicon Dioxide (SiO2)

Blue Quartz with Graphite/Tourmaline Inclusions

Silicon Dioxide (SiO2) with Carbon (C) or Schorl elements

Turquoise

CuAl6(PO4)4(OH)8·4H2O

Green Slag Glass

Cullet (Amorphous Silicon Dioxide with impurities)

Fulgurite

Fulgurite (Lechatelierite-rich fused silica)

Shale

Fissile Mudrock (Clay-rich Sedimentary Rock)

Shale

Mudstone/Shale

Druzy Quartz Geode (with Chalcedony)

Silicon Dioxide (SiO2)

Dyed Agate Geode

Silicon Dioxide (SiO2) with artificial pigment

Green Glass Slag

Amorphous Silicon Dioxide (SiO2) with metal oxide impurities

River Cobble (Diorite or Meta-volcanic with Quartz Veining)

Diorite (with SiO2 quartz veins)

Yellow Chert (Yellow Jasper)

Silicon Dioxide (SiO2)

Quartzite

Quartzite (composed primarily of silica, SiO2)

Polished orbicular jasper (likely ocean jasper)

Jasper, a microcrystalline variety of quartz (SiO₂), with iron-oxide and other mineral inclusions