Igneous Rock

Basalt

Basalt

Basalt with Quartz Veins

Basalt with Quartz or Calcite Veining

Granite

Granite (Plutonic Igneous Rock)

Weathered sandstone or fine-grained graywacke

Clastic sedimentary rock; chiefly quartz (SiO₂), feldspar, and lithic fragments bound by silica, calcite, or iron-oxide cement

Fossilized coral fragment

Fossil scleractinian coral; commonly calcite/aragonite replaced by calcite (CaCO₃)

Granite Pebble

Granite

Quartz in Host Rock

Silicon Dioxide (SiO2) in Rhyolite or Granite matrix

Granite / Igneous Rock Specimen

Phaneritic Igneous Rock

Weathered vesicular basalt (likely amygdaloidal basalt)

Basalt, chiefly plagioclase and pyroxene with possible olivine; cavities may contain secondary zeolites, calcite, or silica

Dark igneous rock, likely basalt or diabase, with a second purplish specimen

Basalt/diabase; exact identification is uncertain from the photograph

Granite-like igneous rock

Likely medium-grained granite or granodiorite; quartz–feldspar–mica aggregate

Porphyritic Igneous Rock / Rhyolite Porphyry

Porphyritic volcanic rock

Porphyritic Igneous Rock / Granite or Rhyolite Porphyry

Porphyritic intrusive/extrusive igneous rock

Granite

Granite

Diorite with Quartz Veins

Diorite

Basalt with Quartz Veins

Amygdaloidal Basalt (matrix) with Crystalline SiO2 (veins)

Porphyritic Igneous Rock / Porphyry

Porphyry (Plagioclase/Quartz phenocrysts in a finer-grained groundmass)

Pink granite (likely weathered or pegmatitic granite)

Granite; chiefly quartz (SiO₂), potassium feldspar, plagioclase, and minor biotite/hornblende

Porphyritic igneous rock, possibly basaltic-andesite

Porphyritic andesite/basalt; likely plagioclase phenocrysts in a fine mafic groundmass

Weathered igneous rock fragment, possibly granite or granitic gneiss

Indeterminate; likely quartz–feldspar–mica aggregate (granite), possibly foliated gneiss

Granite and Igneous Rock Collection

Intrusive igneous rock / Granitoid

Gneiss and Igneous Rock Collection

Foliated Metamorphic Rock (Gneiss) / Igneous Rocks

Porphyritic Igneous Rock / Basalt or Andesite Xenolith in Granite or Quartzite

Silicate rock with contrasting xenolith/inclusion

Likely porphyritic igneous rock (possibly granite or rhyolite)

Quartz–feldspar–mica aggregate; exact identification requires a fresh surface and tests

Possible dark igneous rock

Indeterminate; likely basalt or fine-grained mafic rock

Rounded reddish-brown pebble

Likely ferruginous sandstone or iron-rich quartzite; exact identification requires a fresh surface and tests

Biotite mica schist (probable)

Mica schist, dominated by biotite mica (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂) with quartz and feldspar

Mafic igneous rock, likely basalt or gabbro

Basalt–gabbro composition: chiefly plagioclase feldspar and pyroxene, with possible olivine and iron-titanium oxides

Weathered gray-green igneous rock, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, amphibole, and alteration minerals

Dark igneous rock, likely basalt

Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides

Weathered dark igneous rock, likely basalt

Basalt; commonly composed of plagioclase feldspar, clinopyroxene, and minor olivine or iron oxides

Weathered dark igneous rock, likely basalt

Basalt; primarily plagioclase feldspar and pyroxene, commonly with olivine and iron oxides

Dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides

Weathered dark igneous rock fragment

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

Granite

Granite

Granite

Granite

Dark igneous rock fragment, likely basalt

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

Likely weathered igneous rock fragments

Indeterminate; possibly basaltic or granitic rock with quartz, feldspar, and dark mafic minerals

Weathered dark igneous rock, likely basalt

Basalt, predominantly plagioclase feldspar and pyroxene, with possible olivine and iron oxides

Weathered felsic igneous rock, likely granite or rhyolite

Granite–rhyolite composition; chiefly quartz, alkali feldspar, plagioclase, and minor mica/iron oxides

Coarse-grained mafic igneous rock, likely gabbro

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

Weathered brown-gray igneous rock, likely basaltic andesite

Porphyritic basaltic andesite; probable plagioclase–pyroxene volcanic rock