Organic (Geological Interest)

Limonite Concretion

Limonite (Hydrated iron(III) oxide-hydroxides, FeO(OH)·nH2O)

Pearl (in Marcasite Jewelry)

Biogenic Calcium Carbonate (primarily Aragonite, CaCO3)

Pearl (with Peridot)

Calcium carbonate (CaCO3) + Conchiolin; Peridot: Magnesium iron silicate (Mg, Fe)2SiO4

Possible mafic xenolith in granite

Dark mafic inclusion, likely amphibolite or gabbro, enclosed in coarse-grained granite

Basalt with Caliche Crust

Aphanitic Mafic Igneous Rock with Calcium Carbonate (CaCO3) coating

Limonite with Quartz

FeO(OH)·nH2O (Limonite) with SiO2 (Quartz)

Ironstone Concretion

Ironstone (primarily Siderite or Limonite / Goethite, FeO(OH)·nH2O)

Siltstone with Quartz Vein

Siltstone (composed of Quartz and Clay minerals) with a hydrothermal Quartz vein (SiO2)

Small iron-stained quartz pebble

Quartz (SiO₂), with yellow-brown iron-oxide staining

Sandstone with Iron Staining

Arenite (SiO2 with Fe2O3)

Vesicular basalt

Basalt, likely amygdaloidal or scoriaceous basalt

Limonite (Ironstone)

Limonite (Hydrated iron(III) oxide-hydroxide, FeO(OH)·nH2O)

Granite fragment

Phaneritic Igneous Rock (Granitic composition)

Small gray rock fragment

Indeterminate; possibly quartz-rich granite, chert, or concrete-like silicate material

Dark brown mineral fragments, possibly garnet or iron-rich rock

Indeterminate from image; possible almandine garnet (Fe₃Al₂Si₃O₁₂) or limonite-rich material

Amygdaloidal Basalt

Amygdaloidal Basalt (Mafic volcanic rock)

Granite (likely a weathered granite cobble)

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

Quartz Vein in Pelite (Metamorphic Rock)

Hydrothermal Quartz Veining in Metasedimentary Rock (SiO2)

Sandstone with Foliose Lichen

Arenite (Rock matrix) with Xanthoparmelia or Flavoparmelia (Lichen genus)

Small pale pebble, possibly quartz or feldspar

Unidentified silicate; appearance alone cannot distinguish quartz (SiO₂) from feldspar

Brecciated rock, likely polymict breccia

Polymict breccia; exact lithology cannot be determined from the image

Likely brown ironstone or limonite-rich rock fragment

Ironstone, chiefly iron oxides/hydroxides such as goethite (α-FeO(OH)) and limonite

Basalt with Desert Varnish

Mafic Igneous Rock with Ferromanganese Coating

Limonite

Limonite (Hydrated iron(III) oxide-hydroxide) FeO(OH)·nH2O

Limonite (after Pyrite Pseudomorph)

Limonite (Hydrated Iron Oxide Mixture, FeO(OH)·nH2O)

Quartzite (Ferruginous)

Metamorphosed Quartz Sandstone (SiO2 with Iron oxide staining)

Likely weathered native copper-bearing rock

Unidentified copper-bearing specimen; native copper (Cu) is possible but cannot be confirmed visually

Quartz Pebble

Silicon Dioxide (SiO2)

Quartz with Iron Staining

Silicon Dioxide (SiO2) with Hematite inclusions

Unidentified dark metallic fragment

Possibly iron-rich mineral or metallic meteorite fragment; image is insufficient for a reliable identification

Quartz Vein in Host Rock

Crystalline Silicon Dioxide (SiO2) in Pelitic or Shaly Matrix

Mica Schist

Foliated Metamorphic Rock (rich in Muscovite or Biotite)

Quartz-rich metamorphic rock, likely quartzite or vein quartz

Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with mica and feldspar

Quartz-rich rock, likely milky quartz vein material

Predominantly quartz (SiO₂), with possible iron-oxide staining and dark accessory minerals

Likely metallic ore specimen

Undetermined; the silvery, reflective surface may indicate specular hematite (Fe₂O₃), but the image is insufficient for reliable identification.

Weathered granite

Granite, typically composed of quartz, feldspar, and mica

Iron-stained quartz-rich pebble

Likely quartz with iron-oxide staining; exact identification is uncertain from the image

Brown stone, likely a weathered chert or iron-stained rock

Unidentified brown lithic specimen; composition cannot be determined from the image

Unidentified rock fragments

Indeterminate; likely a weathered, iron-stained silicate rock

Quartz pebble or seed/crumb

SiO2 (if quartz)

Likely ironstone or iron-rich sandstone fragment

Iron-oxide-cemented sandstone; exact mineral composition cannot be confirmed from the photograph

Mica-rich Sandstone or Micaceous Schist Weathering

Micaceous Schist (Muscovite-Quartz composition)