Igneous Rock

Pyrite-bearing dark igneous rock, possibly basalt

Likely basalt or mafic volcanic rock with disseminated pyrite (FeS₂); identification is provisional from the photograph

Weathered feldspar-rich igneous rock, likely granite or granodiorite fragment

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

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

Feldspar-rich igneous rock, likely granite or gneiss fragment

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

Coarse-grained igneous rock, likely granitic pegmatite or weathered granite

Granite/pegmatitic granite; chiefly quartz (SiO₂), feldspar, and dark mica or amphibole

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

Copper-stained quartz/igneous rock specimen

Quartz (SiO₂), with secondary copper minerals; host likely altered volcanic rock

Weathered basalt or dark igneous rock fragment

Likely basalt, a fine-grained mafic volcanic rock; exact identification is uncertain from the image

Weathered dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or magnetite

Basalt (or similar Mafic Igneous Rock)

Basalt

Dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and possibly olivine

Green-speckled igneous rock, likely epidote-bearing basalt or serpentinite

Tentatively epidote-bearing basalt (compositionally uncertain from the image)

Weathered mafic igneous rock, likely basalt

Basalt (fine-grained mafic volcanic rock; exact identification is uncertain from the image)

Dark igneous rock, likely basalt

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

Dark, coarse-grained igneous rock, likely basalt or gabbro

Basalt (fine-grained) or gabbro (coarse-grained), composed mainly of plagioclase feldspar and pyroxene

Dark igneous rock, likely basalt

Basalt; fine-grained mafic rock dominated by plagioclase and pyroxene, with possible olivine and iron oxides

Weathered coarse-grained igneous rock, likely diorite or gabbro

Diorite–gabbro compositional range; chiefly plagioclase feldspar, amphibole/pyroxene, and minor biotite or quartz

Dark igneous rock, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, with possible iron-oxide staining

Weathered igneous rock, likely basaltic lava (uncertain)

Fine-grained mafic volcanic rock, probably basalt; exact identification requires testing

Dark igneous rock, possibly basalt or gabbro

Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, with possible olivine or iron oxides

Weathered gray igneous rock, likely granite or granodiorite

Granite–granodiorite; mainly quartz, feldspar, and mica

Weathered dark igneous rock, likely basalt

Basalt; chiefly plagioclase feldspar and pyroxene, possibly olivine and iron oxides

Coarse-grained igneous rock, likely granite or granodiorite

Granite–granodiorite; chiefly quartz, feldspar, and biotite/hornblende

Weathered metal-rich igneous rock, likely basalt or komatiitic peridotite

Probable altered mafic–ultramafic rock containing pyroxene/amphibole, olivine, iron oxides, and possible metallic sulfides

Porphyritic Igneous Rock with Iron Oxide Weathering

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

Dark weathered igneous rock, likely basalt

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

Peridotite Nodules in Basalt (Xenolith)

Ultramafic Xenolith (Olivine-rich Peridotite in Basalt)

Weathered granitic boulder

Granite, typically composed of quartz, feldspar, and mica

Dark fine-grained igneous rock, likely basalt

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

Fine-grained dark igneous rock, likely basalt

Basalt, composed chiefly of plagioclase feldspar and pyroxene, with possible olivine or magnetite

Coarse-grained gray igneous rock, likely granite or granodiorite

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

Weathered iron-rich concretion or ironstone cobble

Limonite/goethite-rich ironstone, commonly with hematite and quartz

Quartz-bearing dark igneous rock, likely gabbro or basalt

Gabbro/basalt dominated by plagioclase and pyroxene, with minor quartz or calcite

Dark coarse-grained igneous rock, likely gabbro or diabase

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

Tumbled dark igneous rock, likely basalt

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

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

Milky Quartz with Mineral Inclusions

Silicon Dioxide (SiO2) with miscellaneous inclusions

Quartz / Quartzite

Silicon Dioxide (SiO2)