Igneous Rock (Volcanic Glass)

Pumice

Vesicular volcanic glass (Amorphous silica mixed with various oxides)

Weathered metamorphic rock, likely gneiss or schist

Indeterminate foliated silicate rock; commonly quartz–feldspar–mica assemblage

Snowflake Obsidian

Volcanic Glass with Spherulite inclusions (Amorphous SiO2 + Cristobalite)

Pyrite-bearing Rock

Iron Sulfide (FeS2)

Quartz Vein in Host Rock

Silicon Dioxide (SiO2)

Polished dark gray stone, likely basalt or andesite

Fine-grained mafic volcanic rock, commonly basalt (plagioclase ± pyroxene, olivine, and iron oxides)

Tumbled amethyst

Amethyst, purple variety of quartz (SiO₂)

Basalt

Extrusive Igneous Rock

Mahogany Obsidian

Obsidian (Volcanic Glass with Hematite/Magnetite inclusions)

Vesicular Basalt (or Scoria)

Extrusive Igneous Rock (Mafic)

Rounded beach cobble, likely vesicular basalt

Basalt (fine-grained mafic volcanic rock; exact identification uncertain from image)

Possibly tumbled dark stone or mineral specimen

Indeterminate from image; possibly black tourmaline, basalt, or another dark silicate

Basalt

Extrusive Igneous Rock

Olivine Basalt (Pumice or Scoria)

Mafic extrusive igneous rock

Unidentified polished stone or mineral specimen

Indeterminate from the blurred photograph; possibly a polished pale chalcedony, quartz, or feldspar piece

Basalt

Extrusive Igneous Rock

Rounded gray river pebble, likely fine-grained basalt or andesite

Basaltic-andesitic volcanic rock; commonly plagioclase feldspar, pyroxene, and minor iron oxides

Weathered vesicular volcanic rock, likely pumiceous andesite or rhyolite

Pumiceous intermediate-to-felsic volcanic rock; commonly composed of plagioclase, quartz, alkali feldspar, and volcanic glass, with possible iron-oxide staining

Agate Geode

Silicon Dioxide (SiO2) - Chalcedony variety

Obsidian (likely black volcanic glass)

Obsidian; naturally occurring rhyolitic glass, primarily SiO₂

Amygdaloidal Rhyolite

Rhyolite (felsic volcanic rock) with amygdules

Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within Sedimentary or Igneous Matrix

Snowflake Obsidian

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

Agate (Moss or Plume Agate variety)

Silicon Dioxide (SiO2)

Weathered basalt pebble

Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine

Vesicular basalt (possibly scoriaceous basalt)

Basalt; predominantly plagioclase feldspar, clinopyroxene, and Fe-Ti oxides, with possible olivine

Basalt pebble

Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine

Polished basalt pebble (likely vesicular basalt)

Basalt; fine-grained mafic volcanic rock, principally plagioclase and pyroxene with possible olivine and iron oxides

Weathered basalt pebble

Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine

Obsidian

Volcanic glass (SiO2 - Silicon Dioxide with impurities)

Basalt Pebble

Extrusive Igneous Rock

Basalt with Quartz Vein

Mafic volcanic rock with hydrothermal SiO2 filling

Pumice

Vesicular volcanic rock, primarily silica-rich volcanic glass (commonly rhyolitic or dacitic)

Polished dark stone, possibly obsidian

Volcanic glass; likely rhyolitic obsidian (SiO₂-rich, noncrystalline)

Hollow geode or vesicular volcanic rock

Likely quartz-lined basaltic/andesitic vesicle; exact identification requires testing

Dark volcanic sand / basaltic sand

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

Vesicular volcanic rock, likely weathered pumice or scoria

Pumice/scoria; predominantly volcanic glass and feldspar, with possible iron oxides

Polished black stone, likely basalt or dark river pebble

Basalt; chiefly plagioclase feldspar and pyroxene, commonly with minor magnetite

Dalmatian jasper (likely orbicular rhyolite)

Silica-rich rhyolite, commonly sold as Dalmatian jasper; typically quartz, feldspar, and dark amphibole/biotite inclusions

Weathered basalt cobble

Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, with possible olivine and iron oxides

Weathered basalt cobble

Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene with possible olivine and iron oxides

Likely basalt

Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine