Metamorphic (Altered Igneous Rock)

Rounded green-gray river cobble

Likely altered basalt or andesite; exact identification requires a fresh surface and tests

Unakite

Epidotized Granite

Fine-grained dark gray rock core, likely basalt or andesite

Probable basaltic-andesitic volcanic rock; exact identification requires thin section or geochemical testing

Pink feldspar-bearing granite or pegmatitic rock

Granite/pegmatite, chiefly quartz (SiO₂), potassium feldspar (KAlSi₃O₈), plagioclase, and dark mica/amphibole; pink areas may be K-feldspar or garnet.

Dark river-worn stone, likely basalt

Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene

Unakite

Unakitized granodiorite / Quartz-Epidote-Feldspar rock

Weathered iron-rich stone, likely basalt or ironstone

Probable basalt (mafic volcanic rock) with iron-oxide weathering; exact identification requires testing

Iron-stained quartz vein rock

Quartz-rich vein material with iron oxides/hydroxides (quartz, SiO₂, stained by hematite/goethite); likely hosted in a metamorphic rock

Greenstone (Amygdaloidal Basalt)

Amygdaloidal Basalt (frequently composed of Plagioclase Feldspar, Pyroxene, and Olivine with Chlorite inclusions)

Rounded river pebble, probably basaltic-andesite or fine-grained igneous rock

Likely microcrystalline basalt/andesite; exact identification requires testing

Milky quartz vein rock

Quartz-rich hydrothermal vein; predominantly silicon dioxide (SiO₂), with minor iron-oxide staining and possible feldspar or host-rock fragments

Rounded river pebble, likely basalt or weathered andesite

Fine-grained mafic volcanic rock; commonly basalt, approximately plagioclase–pyroxene ± olivine

Quartz-rich rock, possibly milky quartz with chlorite or epidote

Quartz (SiO₂), with unidentified green inclusions

Weathered quartz-rich rock fragment

Indeterminate; likely altered granite or quartz-bearing pegmatite

Hornblende-biotite schist (probable)

Amphibole–biotite schist; chiefly hornblende, biotite, plagioclase, and quartz

Blue-gray quartz-rich pebble, possibly granite or granodiorite

Quartz–feldspar–mica aggregate; likely granodiorite (exact identification requires testing)

Weathered iron-rich volcanic rock

Likely altered basalt or andesite with iron-oxide staining

Green tumbled stone, possibly serpentine

Undetermined; appearance is consistent with serpentine-rich rock (serpentinite), but the image alone cannot confirm identification.

Weathered iron-stained quartz-rich rock, possibly rhyolite or quartzite

Indeterminate silica-rich rock; likely quartz (SiO₂) with iron oxides and clay alteration

Biotite Mica

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

Likely serpentinite

Serpentinite, composed mainly of serpentine-group minerals (such as antigorite or chrysotile)

Unakite

Unakite (Altered Granite)

Weathered volcanic rock, likely basalt

Basalt; primarily plagioclase feldspar, pyroxene, and often olivine

Biotite mica schist fragment

Biotite-rich mica schist; chiefly biotite K(Mg,Fe)3AlSi3O10(F,OH)2 with quartz and feldspar

Quartz-rich metamorphic rock, likely mica schist or gneiss

Quartz–feldspar–mica metamorphic aggregate; exact identification requires thin-section or field tests

Serpentinite (likely serpentinized ultramafic rock)

Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and relict olivine/pyroxene

Copper-bearing quartz/rock fragment with attached mica

Chalcopyrite-bearing quartz or altered igneous rock; attached flake likely muscovite or biotite mica

Porphyritic basalt (likely olivine basalt)

Basalt; fine-grained plagioclase–pyroxene matrix with possible olivine phenocrysts

Vesicular basalt with pink mineral inclusions

Basalt, likely porphyritic/vesicular basalt; inclusions may be calcite, zeolite, or weathered feldspar

Lapis Lazuli

Lapis lazuli (a rock primarily composed of Lazurite: (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2)

Lapis Lazuli

Sodalite-rich metamorphic rock containing Lazurite (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2

Granite (likely weathered, mica-rich granite)

Granite, a coarse-grained quartz–feldspar intrusive igneous rock

Likely serpentinite or chlorite-rich metamorphic rock

Serpentinite, mainly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), possibly with chlorite, magnetite, and carbonates

Weathered greenish mafic rock fragment

Likely altered basalt or basaltic-andesite; exact identification is uncertain from the photograph

Tumbled greenstone / serpentinite (probable)

Serpentinite, chiefly Mg-rich serpentine minerals (antigorite, lizardite, chrysotile), possibly mixed with chlorite, magnetite, or carbonate

Coarse-grained mafic igneous rock, likely gabbro

Gabbro; chiefly calcium-rich plagioclase feldspar and pyroxene, with possible olivine and amphibole

Serpentinized ultramafic rock (likely serpentinite)

Serpentinite; chiefly antigorite/lizardite/chrysotile, commonly after peridotite (olivine–pyroxene)

Porphyritic basalt (likely amygdaloidal basalt)

Basaltic rock dominated by plagioclase feldspar and pyroxene, with possible vesicle-filling zeolite/calcite

Vesicular quartz-rich rock, possibly weathered rhyolite or hydrothermal quartz

Likely quartz (SiO₂) with altered feldspar, iron oxides, and cavities; exact identification requires testing

Vesicular quartz-rich rock, possibly weathered rhyolite or silicified volcanic breccia

Silica-rich volcanic rock; likely microcrystalline quartz (SiO₂) with altered feldspar and iron-oxide staining

Serpentinite

Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), with magnetite and minor chromite/talc

Granite (likely weathered granitic rock)

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