Quartzite (River Pebble)
Meta-quartzite (composed primarily of SiO2)
metamorphic
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River Pebble (Siltstone / Fine Sandstone)
Sedimentary Rock (siliciclastic clastic rock)
sedimentary
Weathered granite fragment
Granite, primarily quartz, feldspar, and mica
igneous
Quartz Vein in Basalt or Slate
Hydrothermal quartz vein traversing mafic host rock
metamorphic
Chert / Flint
Microcrystalline quartz (SiO2)
sedimentary
Coal
Bituminous or sub-bituminous coal (carbonaceous rock)
sedimentary
Fossiliferous Limestone
Bioclastic Limestone (Calcium Carbonate, CaCO3)
sedimentary
Gneiss
Gneiss
metamorphic
Gabbro (or Basalt Pebble)
Mafic Intrusive/Extrusive Igneous Rock
igneous
Basalt
Basalt
igneous
Sandstone or Quartzite
Arenite (if sedimentary) / Quartzite (if metamorphic)
Sedimentary or Metamorphic
Sandstone (Glacial Cobble)
Arenite / Sedimentary Rock (primarily SiO2)
sedimentary
Quartzite Cobble
Metamorphosed Quartz Sandstone (SiO2)
metamorphic
Scoria
Scoria
Igneous
Weathered granitic or gneissic cobble
Likely altered granite/granodiorite; exact identification requires a fresh surface and testing
igneous
Quartz-Veined Gneiss or Metamorphic Rock with Quartz Veins
Quartz-veined metamorphic rock (Silicate mineral assemblage)
metamorphic
Yellow Chert or Jasper
Microcrystalline Quartz (SiO2)
sedimentary
River Pebble (Quartz/Jasper)
Silicon Dioxide (SiO2)
sedimentary
Quartz Pebble
Silicon Dioxide (SiO2)
mineral
Fossiliferous Chert with Brachiopod Impression
Chert (SiO2) containing Brachiopoda fossil remains
sedimentary
Banded Gneiss
Gneiss (Metamorphic Rock)
metamorphic
Shale
Fissile mudrock (composed of clay-sized particles and detrital grains)
sedimentary
Limestone
Sedimentary Calcium Carbonate (CaCO3)
sedimentary
Druzy Quartz on Matrix (likely Limestone or Sandstone)
Silicon Dioxide (SiO2) with various trace impurities
Mineral on Sedimentary Rock
Quartz Vein in Basalt
Silicon Dioxide (SiO2) in Mafic Igneous Rock
igneous
Shale
Shale (claystone/mudstone)
sedimentary
Basalt with Quartz/Calcite Veins
Basalt with hydrothermal vein infill
igneous
Quartz Druzy (on Matrix)
Silicon Dioxide (SiO2)
mineral
Sedimentary Rock with Crafts (Pet Rock)
Sedimentary rock decorated with synthetic materials
sedimentary
Granite
Granite (Felsic Plutonic Rock)
igneous
Rounded quartz-rich pebble
Chert or quartzite pebble (tentative; mostly microcrystalline quartz, SiO₂)
sedimentary
Quartz Crystal Cluster on Matrix
Silicon Dioxide (SiO2)
mineral
Agate
Silicon Dioxide (SiO2) - variety Chalcedony
mineral
Agate (specifically a Yellow/Honey Agate)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
mineral
Quartz Crystal on Matrix
Silicon Dioxide (SiO2)
mineral
Basalt
Basalt (Aphanitic Mafic Igneous Rock)
igneous
Quartz Vein Rock
Quartz (Silicon Dioxide, SiO2)
igneous
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
Metamorphic, likely Sedimentary with Quartz veins
Copper-bearing porphyritic rock (likely bornite/chalcopyrite ore)
Altered porphyritic volcanic rock with copper sulfides, chiefly bornite (Cu₅FeS₄) and/or chalcopyrite (CuFeS₂)
igneous
Eroded Brick or Pumice-like Scoria
Vesicular Basalt / Scoria (Anthropogenic variant: Eroded Firebrick)
igneous
Sandstone
Sandstone (composed predominantly of Quartz, SiO2)
sedimentary
Red Scoria
Scoria (Vesicular Basalt/Andesite)
igneous