Rock

Basalt

Basalt (Aphanitic-fine grained mafic igneous rock)

Polished river pebble

Indeterminate; likely fine-grained quartz-rich sedimentary rock or weathered volcanic rock

Sandstone with Quartz Vein

Arenite with Crystalline Silica (SiO2)

Basalt

Mafic extrusive igneous rock

Shale

Fissile Siliciclastic Sedimentary Rock

Botryoidal Chalcedony (Desert Rose / Agate)

Silicon Dioxide (SiO₂)

Basalt (Vesicular or Porphyritic River Pebble)

Mafic Volcanic Rock (Aphanitic to Porphyritic Basalt)

Greenschist (or Serpentinite) with Quartz-Feldspar Vein

Metabasalt / Greenschist Facies Rock

Quartz pebble

Silicon Dioxide (SiO2)

Milky quartz in dark host rock

Quartz (SiO₂), likely as a vein or vein fragment; host rock uncertain

Copper-bearing porphyritic rock (likely bornite/chalcopyrite ore)

Altered porphyritic volcanic rock with copper sulfides, chiefly bornite (Cu₅FeS₄) and/or chalcopyrite (CuFeS₂)

Shale or Slate with Quartz Veins

Shale (fine-grained clastic sedimentary rock) or Slate (low-grade metamorphic rock formed from shale) with Quartz (SiO2) veins

Granite

Granite (Felsic Plutonic Rock)

Rounded beach pebble

Lithology indeterminate; likely fine-grained sandstone, mudstone, or weathered volcanic rock

Quartz Vein in Siltstone

Silicon Dioxide (SiO2) within Sedimentary/Metamorphic Matrix

Weathered granite or granitic pegmatite

Granite; primarily quartz (SiO₂), feldspar, and mica

Glacial erratic boulder, probably granite or granitic gneiss

Granite–gneiss; mainly quartz, feldspar, and mica

Mica-rich pegmatitic granite

Granitic pegmatite, chiefly quartz, feldspar, and muscovite/biotite mica

Quartz Vein in Host Rock

Quartz (SiO2) in Mafic or Sedimentary Matrix

Grey River Pebble (Greywacke / Basalt)

Stream-rounded silicate rock pebble

Basalt with Quartz/Quartzite Veins

Aphanitic Mafic Volcanic Rock with Siliceous Infillings

Fossilized Oyster Shell

Ostreidae

Mexican Cantera Opal

Amorphous hydrated silica (SiO2·nH2O) in Rhyolitic host rock

Asphalt (Bituminous Slate/Sandstone)

Asphaltum / Bituminous Rock

Granite

Granite (Plutonic Igneous Rock)

Serpentine

Serpentine group (Mg,Fe)3Si2O5(OH)4

Serpentine

(Mg,Fe)3Si2O5(OH)4

Black beach pebble (likely basalt)

Basalt, a fine-grained volcanic rock composed mainly of plagioclase and pyroxene, commonly with olivine

Granite

Granite

Quartz-rich chalcedony (likely silicified rock)

Microcrystalline quartz, SiO₂; possibly silicified limestone or jasper

Weathered quartz pebble (tentative)

Quartz, SiO₂; possibly iron-stained quartz or quartz-rich rock

Weathered banded gneiss

Foliated quartz–feldspar-rich gneiss; exact mineral identification requires closer examination

Quartz geode

Crystalline quartz (SiO₂), lining a geode cavity

Quartz Geode

Crystalline Quartz (SiO2) within a sedimentary/igneous host

Quartz Geode

Silicon Dioxide (SiO2) in a sedimentary or volcanic host

Geode (Unopened)

Siliceous Geode (SiO2)

Red jasper in gray host rock (likely hematite-stained quartzite or rhyolite)

Jasper: microcrystalline quartz (SiO₂), with iron-oxide coloration; exact host uncertain from image

Shale

Shale (clastic sedimentary rock)

Basalt with Weathering Rind

Basalt (Mafic volcanic rock)

Tumbled dark volcanic rock, possibly basalt

Basalt; commonly composed of plagioclase feldspar, pyroxene, and minor olivine or magnetite

Biotite (Black Mica)

Biotite - K(Mg,Fe)3AlSi3O10(F,OH)2

Chert (Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)