Mineral Precipitate (Anthropogenic Context)

Possible obsidian (black volcanic glass)

Obsidian; natural silica-rich volcanic glass, composition typically rhyolitic

Chert Arrowhead (Projectile Point)

Chert (Cryptocrystalline Quartz, SiO2)

Ironstone Concretion (Moqui Marble)

Iron-oxide concretion (Fe2O3 / FeO(OH))

Veined gneiss

Felsic to mafic banded gneiss, chiefly quartz–feldspar–biotite/hornblende

Painted River Rock

Artificially Coated Sedimentary Rock

Quartz-rich hydrothermal specimen, likely milky quartz with calcite

Quartz (SiO₂), with probable calcite (CaCO₃) and iron-oxide staining

Red Sandstone

Arenite (primarily SiO2 with Fe2O3)

Large granite boulder

Granite, a coarse-grained intrusive igneous rock composed mainly of quartz, feldspar, and mica

Granite cobble

Granite, a coarse-grained felsic intrusive igneous rock, chiefly quartz, potassium feldspar, plagioclase, and dark biotite or hornblende

Chalcedony Geode / Agate Nodule

Cryptocrystalline Quartz (SiO2)

Red Sandstone

Arenite (Ferruginous Sandstone)

Citrine

Citrine (Silicon Dioxide, SiO2)

Greenschist

Chlorite Schist (Greenschist Facies)

Baked-clay ceramic fragment (likely brick or pottery)

Fired clay, primarily aluminosilicate minerals; not a natural rock

Chromium (Chrome)

Chromium (Cr)

Chert (Arrowhead/Projectile Point)

Microcrystalline quartz (SiO2)

Obsidian (likely Apache tear or flaked obsidian)

Volcanic glass; primarily rhyolitic silica glass (SiO₂-rich, non-crystalline)

Granitoid (Granite/Gneiss)

Granitoid silicate rock, primarily quartz and feldspar

Tiny amber-colored crystal fragment

Indeterminate; possibly quartz, feldspar, mica, or a sulfide mineral

Ruby (in costume jewelry context)

Corundum (Al2O3) with Chromium impurities

Concrete-like aggregate surface with embedded rock fragments

Anthropogenic concrete or exposed aggregate; not a natural rock specimen

Zebra Jasper

Tetragonal Silicon Dioxide (Quartz) with impurities

Sandstone (Nut-stone / Cup-stone artifact)

Quartz Arenite / Worked Sedimentary Rock

Chert Arrowhead

Microcrystalline Quartz (SiO2)

Greenstone / Greenschist

Greenschist (containing Chlorite, Epidote, Actinolite)

Ironstone concretion

Iron-oxide-cemented sedimentary concretion, commonly hematite/goethite with quartz or clay

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Blue slag glass / industrial smelter slag

Man-made iron-rich silicate slag; composition variable, commonly Fe–Ca–Mg–Al silicates with glassy phases

Iron-rich meteorite candidate

Unclassified meteoritic iron–stone material; possible stony-iron meteorite or terrestrial ironstone

Flint (chert)

Microcrystalline quartz (SiO₂), variety of chert

Hag Stone

Perforated Sedimentary Rock (typically Sandstone or Siltstone)

Mica-rich schist (likely biotite schist)

Biotite–quartz–feldspar schist; mica is chiefly biotite, K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂

Sea Glass

Man-made silicate glass weathering product

Rounded sandstone pebble

Clastic sandstone, predominantly quartz (SiO₂) grains in a cementing matrix

Quartzite Arrowhead

Quartzite (SiO2 silicon dioxide)

Banded Slag Glass (Leland Blue/Frankfort Green style)

Anthropogenic Glass Specimen (Amorphous Silicon Dioxide with impurities)

Sandstone Concretion

Sandstone (Sedimentary Rock) with silica or calcite cement

Chert (Arrowhead/Projectile Point)

Microcrystalline quartz (SiO2)

Chert (Arrowhead)

Chert (SiO2)

Seashell (Cone Snail Shell)

Conus sp. (Calcium Carbonate, CaCO3)

Chert (Arrowhead Fragment)

Microcrystalline Quartz (SiO2)

Bronzite

Enstatite (magnesium iron silicate), (Mg,Fe2+)SiO3