Igneous Rock (Volcanic Glass)

Snowflake Obsidian

Volcanic glass containing Spherulites (SiO2)

Basalt

Extrusive Igneous Rock

Vesicular basalt (probable scoriaceous basalt)

Basalt; chiefly plagioclase, clinopyroxene, and iron-titanium oxides, with possible olivine

Black volcanic rock, possibly basalt or obsidian

Likely basalt (fine-grained mafic silicate rock); obsidian is a possible alternative

Obsidian

Volcanic Glass (Extrusive Igneous Rock, primarily SiO2)

Pumice

Pumice (a highly vesicular volcanic glass)

Banded metamorphic rock, likely gneiss or metasedimentary slate

Quartz–feldspar–mica gneiss (tentative), possibly containing iron-oxide veins

Vesicular basalt (likely scoria)

Basaltic volcanic rock; chiefly plagioclase, pyroxene, and olivine, with possible volcanic glass

Pumice

Pumiceous rhyolite

Obsidian

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

Pumice

Pumice (Vesicular Rhyolite/Andesite)

Apache Tear (Obsidian)

Hydrated volcanic glass (SiO2 with inclusions)

Black obsidian (likely polished)

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

Dark vesicular volcanic rock, likely basaltic scoria

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

Vesicular basalt (possibly scoria)

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

Polished black obsidian

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

Quartz Druze on Matrix

Silicon Dioxide (SiO2)

Weathered vesicular volcanic rock (likely scoria or vesicular basalt)

Vesicular basalt/scoria; primarily plagioclase, pyroxene, olivine, and volcanic glass

Red scoria (vesicular basalt)

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

Likely obsidian (black volcanic glass)

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

Weathered vesicular volcanic rock, likely scoria

Scoria (vesicular basaltic-andesite), compositionally dominated by plagioclase, pyroxene, and iron-rich glass

Porphyry

Porphyritic igneous rock

Likely weathered basalt

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

Pumice

Pumice (Volcanic glass / Silicic extrusive rock)

Snowflake Obsidian

Volcanic glass containing Spherulites of Cristobalite (SiO2)

Basalt

Basalt (Aphanitic Mafic Volcanic)

Pumice

Vesicular Rhyolite / Pumice

Obsidian (Polished)

Obsidian (Volcanic glass, primarily SiO2)

Pumice

Pumice (a highly vesicular volcanic glass)

Vesicular volcanic tuff (likely scoriaceous tuff)

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

Porphyritic Basalt or Porphyritic Andesite

Porphyritic Extrusive Igneous Rock

Obsidian

Volcanic glass (SiO2-rich extrusive igneous rock)

Pumice

Pumice (volcanic glass with vesicular texture)

Pumice

Pumice (Highly vesicular volcanic glass)

Pumice

Pumice (a highly vesicular volcanic glass)

Basalt Pebble

Extrusive Igneous Rock

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

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

Weathered basalt pebble

Basalt, a mafic volcanic rock composed mainly of plagioclase and pyroxene, commonly with olivine and iron-titanium oxides

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

Scoria (vesicular volcanic rock)

Basaltic scoria; chiefly plagioclase, pyroxene, olivine, and iron-rich volcanic glass

Basalt River Cobble

Basalt (Mafic volcanic rock)