Opal
Hydrated Silica (SiO2·nH2O)
mineral
Category
Sedimentary Or Igneous (Secondary Formation)
Browse sedimentary or igneous (secondary formation) specimens identified by the Rock Identifier community.
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Clear Quartz (Rock Crystal)
Silicon Dioxide (SiO2)
mineral
Magnetite
Fe3O4 (Iron(II,III) oxide)
mineral
Gneiss
Gneiss
metamorphic
Quartz-bearing metamorphic rock, likely schist or quartzite
Quartz (SiO₂) in a mica-rich metamorphic matrix
metamorphic
Biotite mica schist (probable)
Schist dominated by biotite mica; commonly quartz–feldspar–biotite
metamorphic
Ferruginous Quartz
Silicon Dioxide (SiO2) with Iron Oxide inclusions
mineral
Likely quartz-rich pebble fragment
Quartz (SiO₂), possibly milky quartz or quartzite; the photo is insufficient to distinguish them confidently
mineral
Blue Apatite
Apatite - Ca5(PO4)3(F,Cl,OH)
mineral
Chalcedony (Grey/White Agate)
Silicon Dioxide (SiO₂)
mineral
Quartz (Druzy)
Silicon Dioxide (SiO2)
mineral
Weathered, biotite-bearing granite or granitic gneiss
Quartz–feldspar–biotite rock; likely granite (compositionally, quartz + K-feldspar/plagioclase + biotite), possibly weakly foliated gneiss
igneous
Blue Apatite
Fluorapatite (Ca5(PO4)3F)
mineral
Magnetite / Hematite mix
Magnetite (Fe3O4) and Hematite (Fe2O3)
mineral
Hematite
Hematite, Iron(III) oxide (Fe2O3)
mineral
Hematite Ball
Iron(III) oxide (Fe2O3)
mineral
Quartz vein in foliated metamorphic rock
Likely quartz-bearing schist or gneiss; visible crystal is quartz (SiO₂)
metamorphic
Weathered, quartz-rich metamorphic rock (likely schist or gneiss)
Quartz–feldspar–mica schist/gneiss, with surface lichens and iron-oxide staining
metamorphic
Psilomelane (Black Hematite/Manganese Ore)
Barium Manganese Oxide (Formula: BaMn9O18(OH)4)
mineral
Tumbled fossiliferous limestone
Micritic limestone, likely bioclastic/fossiliferous carbonate rock (predominantly CaCO₃)
sedimentary
Hematite
Iron(III) oxide (Fe2O3)
mineral
Sulfur
Native Sulfur (S8)
mineral
Milky Quartz
Silicon Dioxide (SiO2)
mineral
Weathered metamorphic rock, possibly schist or gneiss
Indeterminate; likely quartz–feldspar–mica rock, potentially greenschist or gneiss
metamorphic
Blue Quartz (Blue Chalcedony/Dumortierite Quartz)
Silicon Dioxide (SiO2) with inclusions (typically Dumortierite Al7(BO3)(SiO4)3O3)
mineral
Turquoise (possible Dyed Magnesite/Howlite)
CuAl6(PO4)4(OH)8·4H2O
mineral
Chert (Jasper/Agate variety)
Microcrystalline quartz (SiO2)
sedimentary
Hematite
Hematite (Fe2O3)
mineral
Rhodolite Garnet
Magnesium Aluminum Silicate; formula: (Mg,Fe)3Al2(SiO4)3
mineral
Rounded river pebble
Indeterminate lithic clast; likely weathered sandstone or quartz-rich sedimentary rock
sedimentary
Iron-stained milky quartz
Quartz (SiO₂), with iron-oxide staining
mineral
Banded Agate
Chalcedony (Silicon Dioxide, SiO2)
sedimentary
Magnetite / Hematite (Iron Ore)
Magnetite (Fe3O4) or Hematite (Fe2O3)
mineral
Gneiss (Gneissic Granite Pebble)
Metamorphic rock rich in Quartz, Feldspar, and Mica
metamorphic
Banded Gneiss
Gneiss
metamorphic
Weathered brown stone, possibly basalt or iron-rich sedimentary rock
Indeterminate from photograph; likely fine-grained mafic rock (basalt) or ferruginous sandstone
igneous
Jasper (or possibly Agate/Chalcedony) beads
SiO2 (Silicon Dioxide)
mineral
Gold Nugget
Native Gold (Au)
mineral
Garnet-bearing gneiss
Biotite–garnet gneiss, typically quartz + feldspar + biotite + almandine garnet
metamorphic
Magnetite
Magnetite (Fe3O4)
mineral
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral
Quartz-veined metamorphic rock, likely schist or gneiss
Quartz–feldspar–mica rock; exact identification requires testing
metamorphic