Igneous Rock

Basalt

Basalt

Granite

Granite (Plutonic Igneous Rock)

Granite-like igneous rock

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

Granite / Igneous Rock Specimen

Phaneritic Igneous Rock

Porphyritic Igneous Rock / Rhyolite Porphyry

Porphyritic volcanic rock

Granite Pebble

Granite

Porphyritic Igneous Rock / Granite or Rhyolite Porphyry

Porphyritic intrusive/extrusive igneous rock

Porphyritic Igneous Rock / Porphyry

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

Weathered igneous rock fragment, possibly granite or granitic gneiss

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

Quartz in Host Rock

Silicon Dioxide (SiO2) in Rhyolite or Granite matrix

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

Dark igneous rock, likely basalt

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

Dark igneous rock, likely basalt

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

Dark igneous rock fragment, likely basalt

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

Weathered dark igneous rock, likely basalt

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

Tumbled dark igneous rock, possibly gabbro or basalt

Likely mafic rock composed chiefly of pyroxene and plagioclase; exact identification requires testing

Likely coarse-grained igneous rock, possibly granite or gabbro

Granite (quartz–feldspar–mica) or gabbro (plagioclase–pyroxene); exact identification requires a fresh surface and testing

Light-colored igneous rock, likely pumice or vesicular rhyolite

Primarily silica-rich volcanic glass and feldspar; exact identification is uncertain from the photograph

Weathered igneous rock, likely granite or granitic gneiss

Quartz–feldspar–mica aggregate; exact identification requires a fresh surface or testing

Likely weathered igneous rock fragments

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

Feldspar-rich igneous rock, likely granite or gneiss fragment

Granite-like quartz–feldspar rock; exact identification is uncertain from the blurred image

Diorite with Quartz Veins

Diorite

Basalt with Quartz Veins

Amygdaloidal Basalt (matrix) with Crystalline SiO2 (veins)

Basalt (or similar Mafic Igneous Rock)

Basalt

Dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and possibly olivine

Dark igneous rock, likely basalt

Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase and pyroxene, commonly with olivine

Dark weathered igneous rock, likely basalt

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

Porphyritic Igneous Rock with Iron Oxide Weathering

Weathered Porphyry (containing Quartz, Feldspar, Amphibole/Biotite, and Hematite/Limonite)

Coarse-grained gray igneous rock, likely granite or granodiorite

Granite–granodiorite; mainly quartz, feldspar, and mica (exact identification requires testing)

Dark coarse-grained igneous rock, likely gabbro or diabase

Gabbro–diabase; chiefly plagioclase feldspar and pyroxene, with possible olivine and opaque iron-titanium oxides

Rounded reddish-brown pebble

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

Dark gray igneous rock, likely basalt

Basalt; fine-grained plagioclase–pyroxene rock, commonly with minor olivine and magnetite

Tumbled dark igneous rock, likely basalt

Basalt; commonly composed of plagioclase feldspar, pyroxene, and olivine

Coarse-grained gray igneous rock, likely granite or granodiorite

Granite–granodiorite; chiefly quartz, feldspar, and dark mica/amphibole

Biotite mica schist (probable)

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

Dark mafic igneous rock, likely basalt or gabbro

Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine

Fine-grained dark igneous rock, likely basalt

Basalt; predominantly plagioclase feldspar and pyroxene, commonly with minor olivine and iron-titanium oxides

Likely basalt or other dark igneous rock

Basalt; predominantly plagioclase feldspar and pyroxene, possibly olivine