Granite
Granite (Phaneritic intrusive igneous rock) - Composition: SiO2, Al2O3, K2O, Na2O
igneous
Category
Not A Natural Rock
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Dark river-worn cobble, possibly basalt or fine-grained volcanic rock
Likely basaltic rock; exact identification requires a fresh surface and tests
igneous
Dark rounded pebble, possibly basalt
Basalt (fine-grained mafic volcanic rock; identification tentative from photograph)
igneous
Black Onyx
Silicon dioxide (SiO2) - Chalcedony variety
mineral
Black Tourmaline
Schorl (Na(Fe²⁺)₃Al₆(BO₃)₃Si₆O₁₈(OH)₄)
mineral
Sandstone (with possibly iron oxides and other minerals)
Sandstone
Sedimentary rock
Opaline Glass (Opalite)
Synthetic Silicon Dioxide Glass
Mineraloid (Man-made)
Lapis lazuli and green-blue chalcedony jewelry
Lapis lazuli: lazurite-bearing metamorphic rock, chiefly lazurite (Na₃Ca(Al₃Si₃O₁₂)S) with calcite and pyrite; second stone: likely chrysoprase or green-blue chalcedony (microcrystalline quartz, SiO₂)
gemstone
Fossiliferous Limestone
Fossiliferous Calcilutite / Biomicrite
sedimentary
Granite
Granite (a common rock type, not a single mineral with a formula. Composed primarily of quartz, feldspar, and mica/amphibole).
igneous
Dyed Agate
SiO2
Mineral
Dyed Blue Agate
Chalcedony (SiO2) with artificial dye
gemstone
Blue Sapphire (Synthetic or Man-made Glass Imitation)
Corundum (Al2O3) if natural; Lead-glass or Spinal if synthetic
mineral
Prasiolite (Green Quartz) / Sea Glass Amalgam
SiO2 (Silicon Dioxide)
mineral
Citrine Quartz
Silicon Dioxide (SiO2)
mineral
Diamond
Native Carbon (C)
mineral
Titanium Aura Quartz
Titanium-coated Silicon Dioxide (SiO2)
mineral (man-enhanced)
Diamond (or Simulant)
Carbon (C) or relevant simulant formula (e.g., ZrO2 for Cubic Zirconia)
gemstone
Small rounded pebble
Indeterminate lithic grain; likely weathered sandstone, iron-stained quartz-rich rock, or a concretion
sedimentary
Ammonite Fossil
Ammonoidea
fossil
Sandstone
Sandstone (arenite is a more specific geological term for a clean sandstone, while wacke refers to a dirty sandstone with significant matrix)
Sedimentary
Granite
Phaneritic Felsic Igneous Rock (primarily Quartz, Feldspar, and Mica)
igneous
Clear Quartz (Rock Crystal)
Silicon Dioxide (SiO2)
mineral
Iolite (Cordierite)
Cordierite (Mg2Al4Si5O18)
gemstone
Tumbled Chalcedony Pebble
Silicon Dioxide (SiO2)
mineral
Mahogany Obsidian
Volcanic Glass with Hematite or Magnetite (SiO2 + Fe2O3)
igneous
Milky Quartz with Iron Staining
Silicon Dioxide (SiO2)
mineral
Diamond (in Jewelry)
Carbon (C)
gemstone
Obsidian
Volcanic Glass (Amorphous silicon dioxide with trace impurities)
igneous
Tumbled carnelian agate
Cryptocrystalline chalcedony (SiO₂), an iron-colored variety of agate
gemstone
Diamond
C (Carbon)
mineral
Diamond
Diamond (Native Carbon, C)
mineral
Diamond
Carbon (C)
mineral
Diamond
Carbon (C)
mineral
Pebble
Clast (specifically a granule or small pebble)
Sedimentary
Note on Image Identification: Textile
N/A (Anthropogenic material)
not a rock
Carved Stone Turtle
Carved Soapstone and Quartz
mineral
Citrine Quartz
Silicon Dioxide (SiO2) with iron impurities
mineral
Weathered granite or granitic pegmatite cobble
Granite/granitic rock, composed mainly of quartz (SiO₂), feldspar, and minor biotite or other dark minerals; the reddish-brown areas may be iron-oxide staining or weathered accessory minerals
igneous
Quartzite
Quartzite (SiO2)
metamorphic
Diamond
Carbon (C)
gemstone
Turquoise
Hydrated phosphate of copper and aluminum, CuAl6(PO4)4(OH)8·4H2O
mineral