Weathered iron-rich rock, possibly laterite or limonite-bearing quartzite
Limonite/goethite mixture, commonly FeO(OH)·nH₂O, with possible quartz and iron oxides
mineral
Category
Not A Rock (Synthetic Material)
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Plume Agate or Moss Agate
Agate (SiO2)
mineral
Likely weathered igneous rock fragments
Indeterminate; possibly basaltic or granitic rock with quartz, feldspar, and dark mafic minerals
igneous
Polished basalt pebble
Basalt, a fine-grained mafic volcanic rock; chiefly plagioclase, pyroxene, and iron-titanium oxides
igneous
Basalt
Basalt (Mafic volcanic rock)
igneous
Granite
Felsic intrusive igneous rock
igneous
Vuggy Quartz on Matrix
Silicon Dioxide (SiO2)
mineral
Sandstone
Arenite (SiO2 based)
sedimentary
Concrete / Anthropogenic Conglomerate
Man-made composite material (Portland cement, aggregate, and water)
not a natural rock
Asphalt Chunk (with aggregate)
Bituminous concrete / Anthropogenic conglomerate
sedimentary (anthropogenic/man-made conglomerate)
Likely basalt pebble
Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine
igneous
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
Quartz Vein in River Siltstone
Crystalline Quartz (SiO2) in Siliclastic Matrix
sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
sedimentary
Sandstone
Clastic sedimentary rock (primarily quartz arenite)
sedimentary
Likely weathered iron-rich quartz or chert
Microcrystalline quartz (SiO₂), possibly limonite/goethite stained
mineral
Likely quartz-rich river pebble
Milky quartz or quartz-bearing granitic/gneissic fragment (SiO₂-dominant)
igneous
Sandstone
Sandstone (SiO2 dominant)
sedimentary
Quartz cluster, possibly druzy quartz on matrix
Quartz (SiO₂), likely microcrystalline to coarse crystalline; associated matrix uncertain
mineral
Clay Brick
Ceramic structural unit (Al2O3·2SiO2·2H2O as precursor)
metamorphic (man-made/anthropogenic)
Rounded gray-brown pebble
Indeterminate; likely weathered quartz-rich sandstone or fine-grained volcanic rock
sedimentary
Chert
Silicon dioxide (SiO2)
sedimentary
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Sandstone
Clastic Sedimentary Rock
sedimentary
Sandstone
Clastic sedimentary rock
sedimentary
Sandstone
Clastic Sedimentary Rock
sedimentary
Sandstone
Clastic Sedimentary Rock
sedimentary
Sandstone
Clastic Sedimentary Rock
sedimentary
Sandstone
Clastic Sedimentary Rock
sedimentary
Sandstone
Sedimentary Clastic Rock
sedimentary
Amethyst quartz geode
Quartz, SiO₂; purple coloration from irradiation and trace iron
mineral
Sandstone
Clastic sedimentary rock (primarily SiO2)
sedimentary
Sandstone
Arenite (typically SiO2 based)
sedimentary
Sandstone (with potential Concretion or Fossil fragment)
Arenite (primarily SiO2)
sedimentary
Quartz with Mica Schist
Quartz-Mica Schist / Pegmatitic Quartz
metamorphic
Jasper
Silicon Dioxide (SiO2) microcrystalline quartz
sedimentary
Unidentified weathered mineral/rock fragment
Indeterminate; likely a weathered iron-rich silicate or sulfide-bearing specimen
mineral
Rounded basalt cobble
Basalt, aphanitic mafic volcanic rock; commonly plagioclase + clinopyroxene ± olivine and iron-titanium oxides
igneous
Smooth river pebble, likely quartz-rich sandstone or quartzite
Probable quartz arenite (sandstone) or quartzite; mainly SiO₂ with minor iron-bearing minerals
sedimentary/metamorphic
Amygdaloidal Basalt with Quartz
Basalt with Secondary Mineral Infilling
igneous
Quartz (River Pebble)
Silicon Dioxide (SiO2)
mineral
Milky Quartz
Silicon Dioxide (SiO2)
mineral