Igneous Rock (Volcanic Glass)

Obsidian

Volcanic Glass (Amorphous silicon dioxide with trace impurities)

Amethyst

Silicon Dioxide with iron impurities (SiO2)

Vesicular Basalt (Scoria)

Mafic Igneous Volcanic Rock

Vesicular volcanic rock (likely pumice or scoria)

Gas-rich volcanic lava; likely pumice (silica-rich) or scoria (iron-rich)

Black pebble, likely basalt

Basalt, fine-grained mafic volcanic rock; possibly weathered basaltic glass

Pumice

Vesicular volcanic glass (primarily SiO2 with Al2O3)

Pumice

Pumice, a highly vesicular volcanic rock composed mainly of volcanic glass with variable feldspar and silica minerals

Basalt

Extrusive igneous rock

Quartz on Host Rock

Silicon Dioxide (SiO2)

Basalt with Weathering Rind

Basalt (Mafic Volcanic Rock)

Peridotite

Ultramafic igneous rock

Vesicular basalt with a pale mineral fragment

Basalt; predominantly plagioclase, pyroxene, and iron-titanium oxides

Weathered volcanic rock, probably basaltic scoria or vesicular basalt

Vesicular basalt; predominantly plagioclase, clinopyroxene, olivine, and volcanic glass/iron oxides

Basalt

Mafic Igneous Rock

Basalt Pebble

Extrusive Igneous Rock

Likely tumbled black basalt or volcanic glass

Basalt (plagioclase–pyroxene rock), possibly obsidian (volcanic glass)

Polished basalt with chalcedony/agate vein

Basalt (fine-grained mafic volcanic rock) with microcrystalline quartz, SiO₂

Weathered vesicular volcanic rock (likely pumice or scoria)

Vesicular volcanic glass/rock, commonly rhyolitic pumice or basaltic scoria

Porphyry

Porphyritic Igneous Rock

Basalt

Extrusive Igneous Rock

Porphyry

Porphyritic igneous rock

Vesicular Basalt

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Basalt Pebble

Extrusive Igneous Rock

Unidentified dark gray rock fragment

Likely fine-grained basalt or andesite; exact identification requires testing

Weathered basalt or volcanic breccia

Fine-grained mafic volcanic rock, likely basalt (plagioclase–pyroxene ± olivine), possibly brecciated

Pumice

Highly vesicular volcanic rock, typically rhyolitic to andesitic in composition; mainly silica-rich volcanic glass with feldspar and minor quartz or ferromagnesian minerals.

Basalt with Alteration Crust

Basalt (SiO2 range 45-52%)

Weathered granite fragment

Granite, chiefly quartz, alkali feldspar, plagioclase, and mica

Vesicular basalt (likely weathered scoriaceous basalt)

Basalt; predominantly plagioclase, clinopyroxene, and volcanic glass, with possible iron oxides and secondary zeolite minerals

Granite (likely weathered granite or granitic gneiss)

Granite; mainly quartz (SiO₂), feldspar, and mica

Basalt

Aphanitic Mafic Igneous Rock

Scoria

Vesicular Mafic Igneous Rock

Pumiceous volcanic rock (likely rhyolitic pumice/tuff)

Felsic volcanic glass and ash; commonly quartz–alkali feldspar–plagioclase composition

Basalt Pebble

Extrusive igneous rock

Basalt Pebble

Extrusive igneous rock

Basalt River Pebble

Basalt (Mafic Volcanic Rock)

Basalt River Pebble

Basalt (Mafic volcanic rock)

Basalt River Stone

Basalt (Mafic volcanic rock)

Scoria (vesicular volcanic rock)

Basaltic scoria; chiefly plagioclase, pyroxene, olivine, and volcanic glass