Volcanic Glass (Igneous)

Likely black obsidian

Obsidian (natural volcanic glass; typically rhyolitic, silica-rich composition)

Pumice

Vesicular volcanic glass; primarily rhyolitic to dacitic composition, rich in silica (SiO₂)

Pumice

Pumice (Vesicular Rhyolite/Andesite)

Likely obsidian (rough fragment)

Volcanic glass, predominantly silica-rich rhyolitic composition (SiO₂-rich, noncrystalline)

Pumice

Pumice (Volcanic glass / Felsic extrusive rock)

Weathered, vesicular volcanic rock (likely basaltic scoria)

Scoria, probably basaltic; exact identification requires testing

Polished black gemstone, likely obsidian

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

Vesicular volcanic rock, likely pumice or scoriaceous rhyolite

Silica-rich vesicular volcanic rock; commonly rhyolitic pumice (SiO₂-rich glass)

Basalt

Extrusive Igneous Rock

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide)

Snowflake Obsidian

Volcanic glass with Phenocrysts (SiO2 with Cristobalite inclusions)

Agate

Cryptocrystalline quartz, SiO2

Obsidian (likely black obsidian)

Volcanic glass; predominantly rhyolitic silica (SiO₂-rich), noncrystalline

Mahogany Obsidian

Natural Volcanic Glass (SiO2 with iron and magnesium oxides)

Basalt

Extrusive Igneous Rock

Pumice

Pumice (a volcanic glass, primarily SiO2 with Al2O3)

Mahogany Obsidian

Volcanic glass (SiO2 with Hematite or Magnetite inclusions)

Snowflake Obsidian

Volcanic Glass (SiO2 rich with Cristobalite inclusions)

Pumice

Pumice, vesicular volcanic glass; typically silica-rich rhyolitic composition

Pumice

Highly vesicular volcanic glass, commonly rhyolitic or andesitic in composition

Snowflake Obsidian

Volcanic glass with Cristobalite inclusions (mostly SiO2)

Pumice

Vesicular Rhyolite or Dacite Pumice (Amorphous volcanic glass)

Porous volcanic rock (likely scoria)

Scoria, vesicular basaltic to andesitic volcanic rock

Orbicular rhyolite (likely)

Rhyolite, a silica-rich volcanic rock; commonly quartz, alkali feldspar, plagioclase, and iron-rich alteration minerals

Pumice

Highly vesicular rhyolite/dacite (Amorphous glass)

Tumbled black obsidian

Obsidian (volcanic glass), primarily rhyolitic silica glass

Red obsidian (likely mahogany obsidian)

Volcanic glass; primarily silica-rich rhyolitic glass (SiO₂), commonly with iron-oxide inclusions

Rhyolite

Rhyolite (High-silica volcanic rock)

Polished obsidian (likely snowflake obsidian)

Volcanic glass, predominantly silica-rich rhyolite; snowflake obsidian contains cristobalite spherulites

Polished black-and-white stone, possibly snowflake obsidian

Likely obsidian (volcanic glass); exact identification is uncertain from the photo

Obsidian (likely)

Volcanic glass, predominantly silica-rich rhyolitic composition (no fixed mineral formula)

Obsidian

Volcanic Glass (SiO2 - Silicon Dioxide with impurities)

Pumice

Pumicite (Volcanic glass with vesicular texture)

Polished black obsidian

Volcanic glass; predominantly rhyolitic silica (SiO₂), with minor iron, magnesium, and alkalis

Pumice or vesicular volcanic tuff

Pumice: highly vesicular volcanic glass, typically rhyolitic to dacitic; possible tuff: lithified volcanic ash

Porous vesicular volcanic rock (likely scoria)

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

Polished black stone, likely black obsidian

Obsidian (volcanic glass), predominantly rhyolitic silica glass

Snowflake Obsidian

Spherulitic Obsidian (Volcanic Glass with Cristobalite inclusions)

Pumice

Pumice (Vesicular Felsic to Intermediate Volcanic Rock)

Carnelian / Agate

Silicon Dioxide (SiO2) - Chalcedony

Obsidian

Volcanic glass (SiO2 - Silicon Dioxide)

Tumbled mahogany obsidian

Volcanic glass; rhyolitic obsidian, typically SiO₂-rich with iron-oxide inclusions