Volcanic Glass (Igneous)

Obsidian

Obsidian (principally SiO2 + MgO, Fe3O4)

Red scoria (vesicular volcanic rock)

Scoria, typically basaltic to andesitic volcanic rock

Black polished gemstone pendant, likely obsidian

Volcanic glass; primarily SiO₂ (noncrystalline), possibly black spinel or dyed quartz

Polished mahogany obsidian

Volcanic glass (mostly SiO₂), commonly called mahogany obsidian

Amethyst

Silicon Dioxide (SiO2) with trivalent iron (Fe3+) impurities

Obsidian

Volcanic glass (SiO2 - Silicon Dioxide with impurities)

Basalt (likely vesicular basalt)

Basalt; predominantly plagioclase, clinopyroxene, and olivine, with possible volcanic glass

Polished dark stone, possibly obsidian

Unidentified polished specimen; possibly volcanic glass (obsidian, silica-rich natural glass)

Pumice

Vesicular volcanic glass (primarily Alumino-silicates)

Vesicular volcanic rock (likely pumice or scoria)

Pumice/scoria; predominantly volcanic glass and feldspar-rich silicate material

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Dark glassy pebble, possibly volcanic rock

Likely basalt or volcanic glass (var. obsidian), unconfirmed from image

Polished black stone bead, possibly black obsidian

Likely obsidian (natural volcanic glass; composition chiefly silica-rich volcanic glass), but identification is uncertain from the image

Agate

Silicon Dioxide (Chalcedony), SiO2

Black Obsidian

Obsidian (Volcanic glass), 70–75% SiO2

Quartz (Milky/Smoky Crystal fragment)

Silicon Dioxide (SiO2)

Obsidian

Volcanic glass (SiO2 - Silicon Dioxide with impurities)

Pumice

Pumice (Silicic volcanic glass with vesicular texture)

Moss Agate with Jasper

Chalcedony (SiO2 with inclusions)

Black tumbled stone, possibly obsidian

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

Pumice

Highly vesicular volcanic glass (unnamed scientific variant: Rhyolitic/Andesitic Pumice)

Red Scoria

Scoria (Vesicular Basalt)

Tumbled black stone, likely black obsidian or slag glass

Obsidian (volcanic glass), tentatively; composition commonly rhyolitic, rich in silica

Black obsidian arrowhead

Obsidian; volcanic glass, typically rhyolitic in composition (mostly SiO₂)

Pumice

Highly vesicular volcanic glass, typically rhyolitic to andesitic composition; mainly silicate glass with feldspar, quartz, and minor pyroxene/amphibole.

Snowflake Obsidian

Spherulitic Obsidian (primarily SiO2)

Agate in Matrix

Silicon Dioxide (SiO2) within host rock

Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Obsidian (likely rough black volcanic glass)

Obsidian; predominantly rhyolitic volcanic glass, commonly near SiO₂-rich composition

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide, SiO2)

Black obsidian

Volcanic glass, primarily silica-rich rhyolitic composition (approximately 70–80% SiO₂)

Chalcedony (Quartz Var.)

Silicon Dioxide (SiO2)

Pumice

Pumice (Vesicular intermediate to felsic volcanic glass)

Black Obsidian

Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide) with impurities

Pumice (likely)

Vesicular volcanic rock, typically rhyolitic to dacitic glass with minor feldspar and other minerals

Vesicular volcanic rock, likely pumice

Pumice (highly vesicular volcanic glass; composition commonly rhyolitic to andesitic)

Snowflake Obsidian

Volcanic glass containing Spherulites of Cristobalite (SiO2)

Jasper Agate (Chalcedony)

Silicon Dioxide (SiO2)

Polished black obsidian

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

Mahogany Obsidian

Volcanic Glass (Amorphous Silicon Dioxide with Hematite inclusions)

Mahogany Obsidian

Volcanic Glass with Hematite inclusions (SiO2 + Fe2O3)

Chalcedony (Agate)

Silicon Dioxide (SiO2)