Igneous Rock (Volcanic Glass)

Vesicular basalt (possibly scoria)

Basalt; predominantly plagioclase, pyroxene, and olivine, with vesicles formed by escaping gas

Pumice

Pumice (Vesicular Rhyolite/Andesite)

Red scoria (vesicular basalt)

Scoriaceous basalt; chiefly plagioclase, pyroxene, and iron-rich volcanic glass

Obsidian

Volcanic Glass (Extrusive Igneous Rock, primarily SiO2)

Tumbled black stone, likely basalt or obsidian

Uncertain; likely fine-grained basalt (plagioclase–pyroxene) or dark volcanic glass (obsidian)

Pumice

Pumice (Volcanic glass / Silicic extrusive rock)

Basalt

Extrusive Igneous Rock

Snowflake Obsidian

Volcanic glass containing Spherulites of Cristobalite (SiO2)

Rounded gray pebble, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; commonly basalt (plagioclase ± pyroxene/olivine)

Black obsidian (likely polished)

Volcanic glass; chiefly rhyolitic silica-rich glass (approximately 70–80% SiO₂)

Pumice

Pumiceous rhyolite

Pumice

Pumicite

Snowflake Obsidian

Vitreous Silica with Spherulite inclusions (Amorphous SiO2)

Vesicular basalt (likely scoria or weathered pumice)

Vesicular basalt; chiefly plagioclase, pyroxene, olivine, and volcanic glass

Vesicular volcanic tuff (likely scoriaceous tuff)

Lithified pyroclastic rock composed chiefly of volcanic ash, glass, and lithic fragments

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Polished black obsidian

Volcanic glass; primarily silica-rich rhyolitic composition (SiO₂)

Dark vesicular volcanic rock, likely basaltic scoria

Scoria (vesicular basalt; composition commonly plagioclase, pyroxene, and iron-rich glass)

Scoria (Lava Rock)

Vesicular Basalt / Scoria

Pumice

Pumice (volcanic glass with vesicular texture)

Obsidian

Volcanic glass (SiO2-rich extrusive igneous rock)

Volcanic scoria (likely)

Scoria, a vesicular basaltic to andesitic volcanic rock

Obsidian

Volcanic glass (silica-rich rhyolitic melt; primarily SiO₂)

Red vesicular volcanic rock, likely scoria

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

Basalt

Extrusive Igneous Rock

Pumice

Pumice

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

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

Tumbled gray stone, likely quartzite or fine-grained basalt

Provisional identification: quartzite (mostly microcrystalline SiO₂) or basalt (plagioclase–pyroxene aggregate)

Likely obsidian (black volcanic glass)

Obsidian; predominantly rhyolitic volcanic glass, often ~70–75% SiO₂

Quartz Druze on Matrix

Silicon Dioxide (SiO2)

Weathered, vesicular volcanic rock (likely pumice/scoria)

Pumice or scoriaceous basalt; composition likely volcanic glass with feldspar, pyroxene, and minor iron oxides

Light-colored igneous rock, likely pumice or vesicular rhyolite

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

Pumice or vesicular volcanic rock

Pumice; chiefly volcanic glass (silica-rich, composition commonly rhyolitic to dacitic)

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions

Pumice

Vesicular Rhyolite / Pumice

Vesicular volcanic rock, likely pumice

Pumice; highly vesicular volcanic glass, commonly rhyolitic to dacitic in composition

Vesicular volcanic rock, likely pumice or scoria

Pumice/scoria; predominantly volcanic glass with plagioclase, pyroxene, and/or olivine

Likely weathered basalt

Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, often with minor olivine

Quartz crystals on Basalt

SiO2 (Quartz) on Mafic Igneous Rock (Basalt)

Vesicular volcanic rock, likely pumice or scoria

Pumice (highly vesicular rhyolitic–dacitic volcanic glass) or scoria (vesicular basaltic rock)

Basalt Pebble

Extrusive Igneous Rock

Porphyry

Porphyritic igneous rock