Igneous Rock (Volcanic Glass)

Weathered conglomeratic volcanic rock

Likely basaltic volcanic breccia or agglomerate, with plagioclase, pyroxene, volcanic glass, and lithic fragments

Weathered vesicular volcanic rock, likely basaltic scoria

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

Obsidian

Volcanic Glass (Amorphous Silica)

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Basalt with vesicles/amygdules

Basalt (containing volcanic glass and plagioclase)

Obsidian

Amorphous volcanic glass (primarily SiO2)

Snowflake Obsidian

Obsidian with Cristobalite inclusions (70–75% SiO2)

Pumice

Pumice (Vesicular Felsic Glass)

Snowflake Obsidian

Obsidian with Spherulitic Cristobalite (SiO2)

Pumice

Pumice (a highly vesicular volcanic glass)

Pumice

Pumice (Vesicular volcanic glass / Rhyolite or Trachyte)

Iron-rich, vesicular volcanic rock (possibly scoria)

Scoria, likely basaltic; exact identification requires examination and testing

Polished black stone, likely basalt or black jasper

Indeterminate; possible fine-grained basalt (plagioclase–pyroxene) or black jasper/microcrystalline quartz

Pumice

Pumice (a highly vesicular volcanic glass)

Pumice or vesicular volcanic tuff

Pumice: highly vesicular volcanic glass, chiefly rhyolitic to dacitic; possible tuff: lithified ash and pumice fragments

Polished snowflake obsidian

Obsidian, volcanic glass (SiO₂-rich rhyolitic composition) with cristobalite spherulites

Vesicular Basalt

Extrusive Mafic Volcanic Rock

Likely weathered basalt or andesite fragment

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene ± olivine

Polished black pebble, likely basalt

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

Basalt with Plagioclase or Quartz Inclusion

Melanocratic Basalt with Porphyritic Inclusion

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Agate (Carnelian Agate with Quartz Matrix)

Silicon Dioxide (SiO2)

Obsidian

Volcanic Glass (High silica amorphous rock)

Pumice

Pumice (Vesicular volcanic glass)

Pumice

Pumice (Felsic volcanic glass)

Obsidian

Volcanic Glass (Amorphous Silica)

Pumice

Highly vesicular volcanic rock, typically rhyolitic to andesitic in composition

Snowflake Obsidian

Volcanic glass with Spherulite inclusions (SiO2)

Granite and Pumice

Granite (plutonic rock) and Pumice (volcanic glass)

Pumice

Pumicite

Vesicular volcanic rock, likely scoria

Scoria (vesicular basaltic to andesitic volcanic rock)

Pumice

Vesicular Rhyolite or Dacite Pumice (Amorphous volcanic glass)

Chalcedony (Agate/Quartz)

Silicon Dioxide (SiO2)

Obsidian (Black)

Obsidian (approx. 70–75% SiO2)

Blue Obsidian

Volcanic Glass (SiO2 with inclusions)

Obsidian Arrowhead

Volcanic Glass (Amorphous Silicon Dioxide)

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide)

Porous vesicular volcanic rock (likely scoria)

Scoria; chiefly iron-rich volcanic glass with plagioclase, pyroxene, and/or olivine

Moss Agate with Jasper

Chalcedony (SiO2 with inclusions)

Rounded river cobble, likely basalt or weathered andesite

Fine-grained mafic volcanic rock; likely basalt (plagioclase ± pyroxene/olivine)

Obsidian

Volcanic Glass (Silica / SiO2)

Obsidian / Volcanic Glass

Obsidian (principally SiO2, usually 70% or more)