Metamorphic (Low Grade)

Biotite-rich gneiss

Foliated quartz–feldspar–mica gneiss; mainly quartz, plagioclase/alkali feldspar, and biotite

Fine-grained green-gray rock pebble, likely basalt or greenstone

Probable basalt (plagioclase and pyroxene), possibly altered to greenstone

Amazonite

Microcline Feldspar (KAlSi3O8)

Tiger's Eye

Quartz pseudomorph after Crocidolite (SiO2 with Fe oxide inclusions)

Banded Jasper (Chert)

Silicon Dioxide (SiO2)

Epidote

Epidote (formula: Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))

Ferruginous Sandstone

Clastic Sedimentary Rock (Iron-rich)

Polished tiger’s-eye

Chatoyant quartz (microcrystalline quartz, SiO₂, with fibrous riebeckite/crocidolite pseudomorphs)

Epidote

Epidote Group (Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH))

Nephrite Jade

Ca2(Mg,Fe)5Si8O22(OH)2 (Actinolite-Tremolite series)

Pyrite (Fool's Gold)

Iron Sulfide (FeS2)

Serpentinite (often containing Jadeite/Nephrite)

Antigorite-rich Serpentine Rock, (Mg, Fe)3Si2O5(OH)4

Anthracite Coal

Anthracite (Carbon-rich metamorphic rock)

Prehnite

Ca2Al2Si3O10(OH)2

Banded gneiss (polished/tumbled cobble)

Gneiss, composed chiefly of quartz, feldspar, and mica/amphibole

Rough Ruby (Corundum) in Zoisite Matrix

Al2O3 (Aluminum Oxide) with Ca2Al3(SiO4)3(OH)

Weathered greenstone (probable)

Chlorite–actinolite–epidote metamafic rock; exact identification requires testing

Greenstone (likely metamorphosed mafic rock)

Probable chlorite–actinolite–epidote-rich metabasalt; exact identification requires testing

Weathered slate

Slate, a fine-grained metamorphic rock composed mainly of clay-derived mica minerals and quartz

Greenschist (likely chlorite schist)

Greenschist-facies metamorphic rock; commonly quartz + chlorite ± actinolite, epidote, albite, and mica

Greenstone (likely altered basalt or serpentinite)

Chlorite–epidote amphibolite/greenschist or serpentinite; exact identification requires testing

Greenstone / altered basalt (probable)

Chlorite–epidote–actinolite aggregate; commonly metabasalt (greenstone)

Tumbled gray stone, likely slate or fine-grained metamorphic rock

Probable slate/phyllite; composition mainly quartz, mica, and feldspar

Epidote-rich rock (likely epidotite or altered basalt)

Epidote, Ca₂(Al,Fe³⁺)₃(SiO₄)₃(OH); possibly epidote-bearing mafic rock

Likely chlorite-bearing schist (possibly greenschist)

Chlorite–quartz–mica schist; commonly contains muscovite/biotite and feldspar

Tiger’s-eye (likely red/brown variety)

Chatoyant quartz, chiefly SiO₂, pseudomorphous after crocidolite (riebeckite)

Blue-gray metamorphic rock, likely slate or phyllite

Slate/phyllite; chiefly quartz, muscovite/illite, chlorite, and minor feldspar

Anthracite Coal

Anthracite (Carbon)

Quartz with Chlorite / Greenschist

Quartz vein in Greenschist (SiO2 with Chlorite group minerals)

Banded Slate or Siltstone with Quartz/Calcite Veins

Protolith-derived Siltstone or Slate (varies based on degree of metamorphism)

Likely slate or fine-grained schist

Metamorphosed mudstone; commonly quartz–mica–chlorite, with slate dominated by aligned clay minerals

Weathered greenstone / altered rock fragment

Probable chlorite–epidote–actinolite-rich metavolcanic rock; exact identification requires testing

Serpentinite

Serpentinite (complex of Antigorite, Lizardite, and Chrysotile, Mg3Si2O5(OH)4)

Weathered basalt or mafic metavolcanic rock

Basalt, possibly altered to greenstone (chlorite–epidote–actinolite assemblage)

Weathered quartz-rich pebble, possibly metasandstone

Quartz-rich metasandstone (provisional); mainly SiO₂ with minor feldspar, mica, or iron oxides

Likely chlorite schist or altered mafic rock

Chlorite–actinolite schist; commonly composed of chlorite, actinolite/amphibole, epidote, and albite

Polished greenstone pebble (likely epidote-bearing stone)

Epidote–chlorite amphibolite or altered basalt; composition likely epidote, chlorite, amphibole/pyroxene, and iron oxides

River Cobble (likely Metasedimentary)

Metasedimentary Rock / Quartz-rich Sandstone

Waterworn greenstone pebble

Likely serpentinite or chlorite-rich metamorphic rock; exact identification requires testing

Greenstone / Greenschist

Greenschist (composed primarily of Chlorite, Epidote, and Actinolite)

Banded Iron Formation (BIF) / Tiger Iron

Ferruginous Chert (primarily Quartz [SiO2] and Hematite/Magnetite [Fe2O3/Fe3O4])

Greenstone

Greenschist (metamorphosed mafic igneous rock)