Volcanic Glass (Igneous)

Polished mahogany obsidian

Volcanic glass, chiefly rhyolitic in composition (SiO₂-rich amorphous silicate)

Dark volcanic sand / basaltic sand

Basalt-derived lithic sand, chiefly plagioclase, pyroxene, and volcanic glass

Rounded river cobble, likely basalt or weathered andesite

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

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions (SiO2)

Vesicular basalt (likely scoriaceous basalt)

Mafic volcanic rock, chiefly plagioclase, pyroxene, and olivine; commonly iron-rich volcanic glass

Rhyolitic jasper or iron-stained chert

Microcrystalline quartz (SiO₂), likely with hematite/goethite staining

Milky Quartz

Silicon Dioxide (SiO2)

Pink-orange quartz-rich rock, likely rhyolite or jasper

Probable rhyolite (microcrystalline quartz and feldspar), possibly jasper/chalcedony

Black obsidian

Volcanic glass; predominantly rhyolitic silica-rich melt (approximately 70–80% SiO₂), lacking crystalline structure

Snowflake obsidian

Volcanic glass (mostly silica-rich obsidian) with cristobalite spherulites

Mahogany Obsidian

Volcanic Glass (predominantly SiO2 with Fe2O3 inclusions)

Possible obsidian or slag glass

Volcanic glass, primarily SiO₂; alternatively industrial iron-rich glassy slag

Vesicular basalt (likely scoria)

Basaltic volcanic rock; primarily plagioclase, clinopyroxene, olivine, and volcanic glass

Likely vesicular basalt (scoria-like fragment)

Basaltic volcanic rock; chiefly plagioclase, clinopyroxene, olivine, and volcanic glass

Polished mahogany obsidian (probable)

Volcanic glass; chiefly rhyolitic silica-rich glass (SiO₂), compositionally near rhyolite

Mahogany Obsidian

Obsidian (volcanic glass with hematite/magnetite inclusions)

Pumice

Pumice (Volcanic glass / Silicic extrusive rock)

Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Snowflake Obsidian

Volcanic Glass with Cristobalite inclusions (70–75% SiO2)

Obsidian

Obsidian (volcanic glass), predominantly Silicon Dioxide (SiO2)

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite (SiO2 + Fe2O3)

Black obsidian

Volcanic glass; predominantly rhyolitic silica glass (approximately 70–80% SiO₂)

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Obsidian (specifically Mahogany Obsidian)

Volcanic glass (high silica content, SiO2)

Black Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Basalt

Extrusive igneous rock primarily composed of plagioclase feldspar and pyroxene

Black obsidian (likely polished)

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

Vesicular basalt (likely scoria)

Basaltic volcanic rock; predominantly plagioclase, pyroxene, and olivine with volcanic glass

Vesicular basalt (possibly scoriaceous basalt)

Mafic volcanic rock; primarily plagioclase, clinopyroxene, olivine, and volcanic glass

Tektite (Indochinite)

Tektite (SiO2 + Al2O3, Glassy Melts)

Mahogany Obsidian

Volcanic Glass (SiO2 with Hematite/Magnetite inclusions)

Mahogany Obsidian

Volcanic glass (SiO2 with Hematite/Magnetite inclusions)

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide , SiO2)

Pumice

Pumiceous rhyolite

Vesicular volcanic rock, likely scoria

Scoria; basaltic to andesitic volcanic rock, mainly plagioclase, pyroxene, and volcanic glass

Granite and Pumice

Granite (plutonic rock) and Pumice (volcanic glass)

Snowflake Obsidian

Volcanic glass containing Spherulitic inclusions (SiO2 + impurities)

Black Obsidian

Volcanic Glass (Amorphous Silicon Dioxide, SiO2)

Obsidian

Volcanic Glass (SiO2, usually 70% or more)

Scoria (volcanic cinder)

Scoria, vesicular basaltic-to-andesitic volcanic rock

Quartz Druzy (on Geode Fragments)

Silicon Dioxide (SiO2)

Milky Quartz

Silicon Dioxide (SiO2)