Unknown (Likely Sedimentary Or Metamorphic)

Tumbled gneiss (likely biotite gneiss)

Gneiss; quartz–feldspar–biotite assemblage

Banded gneiss (probable)

Quartz–feldspar–mica gneiss; composition commonly dominated by quartz, feldspar, and biotite/hornblende

Quartz (Gray/Smoky Varieties)

Silicon Dioxide (SiO2)

Banded gneiss

Gneiss, likely quartz–feldspar–mica gneiss

Weathered granitic rock (likely granite or granodiorite)

Granite–granodiorite; mainly quartz, feldspar, and mica/hornblende

Banded gneiss (likely weathered paragneiss)

Gneiss; quartz–feldspar–mica ± amphibole assemblage

Gneiss

High-grade metamorphic rock (Gneiss)

Banded Gneiss

Gneiss (complex metamorphic silicate rock)

Weathered sandstone or metasedimentary rock

Quartz-rich sandstone; possibly weakly metamorphosed quartzite

River Pebble (Gneiss or Granite)

Metamorphic Rock (likely Gneiss or Granitic composition)

Quartz-rich metamorphic rock, likely mica schist or quartzite

Quartz (SiO₂) with probable mica, feldspar, and dark accessory minerals

Tumbled quartz-rich rock, possibly calcite or sandstone

Indeterminate from photograph; likely microcrystalline quartz (SiO₂) or calcite (CaCO₃)

Exposed aggregate concrete (stone-chip surface)

Portland-cement concrete containing natural aggregate; not a natural rock

Milky quartz

Quartz (silicon dioxide, SiO₂)

Banded gneiss (likely weathered orthogneiss)

Gneiss; predominantly quartz–feldspar–mica, with possible iron-oxide staining

River Stones (Quartzite and Sandstone)

Quartzite / Sedimentary Rock (SiO2 dominant)

Turquoise (Dyed Howlite/Magnesite imitation)

CuAl6(PO4)4(OH)8·4H2O (Target mineral) / MgCO3 (Magnesite substrate)

Small tumbled quartz-like pebble

Likely quartz (SiO₂), possibly iron-stained chalcedony or feldspar

Rounded greenish pebble

Indeterminate; possibly altered basalt, greenstone, or fine-grained serpentinite

Quartz Pebble

Crystalline Silicon Dioxide (SiO2)

Banded gneiss

Gneiss, likely biotite–quartz–feldspar gneiss

Weathered quartz-rich rock, possibly quartzite or silicified sandstone

Quartzite (mostly SiO₂), with possible iron-oxide staining and minor feldspar/mica

Limonite after Pyrite (Prophecy Stone or Ironstone Concretion)

Goethite/Limonite pseudomorph after Pyrite/Marcasite (FeO(OH)·nH2O)

Glacially rounded metamorphic boulder

Likely foliated amphibolite or gneiss; exact identification requires a fresh surface and mineral examination

Coarse-grained metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss (probable; exact identification requires a fresh surface and tests)

Gneiss (Gneissic Granite)

Gneiss

River Pebble (Gneiss or Quartzite variant)

Metamorphic rock specimen (likely Quartzite or Gneiss)

Dark metamorphic rock, likely schist or slate fragment

Indeterminate; possibly biotite schist, chlorite schist, or slate

Red Jasper

Jasper (Silicon Dioxide with Iron Oxide inclusions, SiO2)

Green calcite (probable)

Calcite, calcium carbonate (CaCO₃)

Banded gneiss pebble

Gneiss, commonly quartz–feldspar–biotite gneiss

Quartzite river stone

Quartzite (SiO2 silicon dioxide)

Tumbled golden-brown stone, likely sandstone or iron-stained quartzite

Indeterminate from image; probable quartz-rich sandstone (SiO₂) or quartzite

Banded gneiss cobble

Gneiss, commonly quartz–feldspar–biotite gneiss

Pyrite-bearing metamorphic rock (likely pyrite schist or quartz–pyrite ore)

Pyrite (FeS₂) in a quartz–mica-rich matrix; exact host rock is uncertain from the image

Tumbled quartz-rich stone, possibly chert or quartzite

Quartzite (mostly SiO₂), though precise identification is uncertain from the image

Weathered quartz-rich metamorphic rock, likely quartzite

Quartzite (mostly microcrystalline quartz, SiO₂), possibly altered sandstone

Tumbled quartz-rich stone, likely milky quartz

Quartz (SiO₂), possibly iron-stained milky quartz or quartzite

Dark mica-rich metamorphic rock, likely schist

Mica schist, probably biotite–muscovite schist; exact identification requires testing

Weathered gray metamorphic rock, likely schist or slate

Foliated silicate rock; possibly mica schist or phyllite

Gneiss Pebble

Gneiss (High-grade metamorphic rock)

Likely quartz-rich metamorphic rock (quartzite or quartz-veined schist)

Quartzite/siliceous schist; chiefly quartz (SiO₂), with probable mica and iron-oxide staining