Igneous Rock (Volcanic Glass)

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Xenolith in Basalt

Mafic Igneous Rock with Felsic Inclusion

Basalt

Extrusive Igneous Rock

Weathered volcanic rock, likely basalt

Basalt; commonly composed of plagioclase, pyroxene, and iron-rich oxides

Quartz Druzy (on Geode Fragments)

Silicon Dioxide (SiO2)

Quartz Geode Fragment

Silicon Dioxide (SiO2)

Slag (Industrial Glass/Glassy Rock)

Anthropogenic Vitreous Material

Snowflake Obsidian

Spherulitic Volcanic Glass (primarily SiO2 with Cristobalite inclusions)

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurities)

Obsidian

Volcanic Glass (SiO2, usually 70% or more)

Vesicular volcanic rock (likely pumice or scoria)

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

Vesicular volcanic rock, likely scoria

Scoria; predominantly basaltic or andesitic volcanic glass with plagioclase, pyroxene, and possible iron oxides

Vesicular volcanic rock, likely pumice or scoria

Vesicular rhyolitic–andesitic volcanic rock; predominantly silicate glass with feldspar and possibly pyroxene

Weathered basalt or andesite

Fine-grained volcanic rock, likely basaltic-andesite; chiefly plagioclase feldspar, pyroxene, and possibly olivine or volcanic glass

Obsidian-like volcanic glass (likely slag or natural obsidian)

Obsidian, primarily amorphous volcanic silica glass (approximately SiO₂); identification is uncertain from an image

Pumice

Pumice (a highly vesicular volcanic rock)

Chalcedony (Grey/White Agate)

Silicon Dioxide (SiO₂)

Vesicular volcanic rock, likely scoria

Scoria (mafic volcanic vesicular basalt), chiefly plagioclase, pyroxene, olivine, and volcanic glass

Vesicular volcanic rock, likely pumice or scoriaceous basalt

Pumice (highly vesicular volcanic glass) or vesicular basalt; exact identification requires testing

Likely raw mica-bearing mineral fragment

Possibly biotite mica or a biotite-rich metamorphic fragment; identification is limited by the dark, blurred image

Weathered volcanic rock, likely andesite or basalt

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, amphibole, and iron oxides

Weathered rhyolitic tuff or altered volcanic rock

Felsic volcanic tuff, likely devitrified or hydrothermally altered

Dark mafic rock, likely basalt

Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or iron oxides

Polished dark stone, likely basalt or gabbro

Basalt (fine-grained mafic rock), possibly gabbro; chiefly plagioclase and pyroxene with iron-magnesium minerals

Yellow chalcedony or quartz fragment

Microcrystalline quartz, SiO₂ (tentative; possibly iron-stained chalcedony)

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide)

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide)

Likely weathered basalt or andesite fragment

Fine-grained volcanic rock, likely basaltic-andesite; exact identification requires testing

Pumice (likely basaltic pumice/scoria)

Vesicular volcanic rock, commonly basaltic; mainly plagioclase, pyroxene, and volcanic glass

Small rounded pebble, likely basalt

Fine-grained mafic volcanic rock (likely basalt); image alone cannot confirm composition

Dalmatian Jasper

Peralkaline Quartz-Feldspar Rock with Arfvedsonite

Black Obsidian

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

Pumice

Highly vesicular volcanic rock, commonly rhyolitic to dacitic glass (SiO₂-rich volcanic material)

Obsidian

Obsidian (volcanic glass), amorphous SiO2 + impurities

Snowflake Obsidian

Volcanic glass containing Spherulitic Cristobalite (SiO2)

Scoria (vesicular volcanic rock)

Basaltic scoria; primarily plagioclase, pyroxene, olivine, and volcanic glass

Pumice

Pumice (a highly vesicular extrusive igneous rock)

Weathered basaltic rock

Basalt, chiefly plagioclase feldspar, clinopyroxene, and minor olivine or iron oxides

Dark gray weathered pebble, likely basalt

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron oxides

Dark Agate / Chalcedony

Microcrystalline Quartz (SiO2)

Clear Quartz (Rock Crystal)

Silicon Dioxide (SiO2)

Weathered porphyritic volcanic rock

Likely porphyritic andesite or dacite, with plagioclase phenocrysts in a fine-grained volcanic groundmass