Igneous Rock (Volcanic Glass)

Basalt Pebble

Extrusive Igneous Rock

Vesicular basalt (scoria-like lava rock)

Vesicular basalt; chiefly plagioclase, pyroxene, olivine, and volcanic glass

Basalt Pebble

Extrusive Igneous Rock

Porphyritic basalt (likely porphyritic andesite)

Plagioclase-phyric volcanic rock; plagioclase phenocrysts in a dark, fine-grained groundmass

Scoria (vesicular volcanic rock)

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

Quartz (Milky/Common)

Silicon Dioxide (SiO2)

Weathered volcanic rock, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; probable basalt (plagioclase ± pyroxene, with alteration minerals)

Rounded basalt pebble

Basalt; fine-grained mafic volcanic rock, commonly dominated by plagioclase and pyroxene with minor olivine

Vesicular basalt (likely weathered basalt cobble)

Basalt; primarily plagioclase, pyroxene, and sometimes olivine

Polished porphyritic basalt (likely)

Basalt, a fine-grained mafic volcanic rock; visible inclusions may be olivine, feldspar, or vesicle infillings

Basalt with Quartz Vein

Extrusive Igneous Rock with Silicon Dioxide Vein

Rounded gray-green pebble, likely basalt or fine-grained metamorphic rock

Probable basalt (plagioclase–pyroxene–iron oxide aggregate); exact identification requires testing

Basalt with Quartz/Calcite Veins

Amygdaloidal Basalt (SiO2 or CaCO3 inclusions)

Vesicular basalt (possibly slag-like volcanic rock)

Basalt, predominantly plagioclase–pyroxene–olivine; exact identification is uncertain from the photograph

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

Basalt

Mafic extrusive igneous rock

Dalmatian Jasper

Peralkaline Quartz-Feldspar Rock with Arfvedsonite

Iron-stained Milky Quartz

Silicon Dioxide (SiO2) with iron oxide inclusions

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

Hollow geode or vesicular volcanic rock

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

Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within Sedimentary or Igneous Matrix

Pumice

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

Porphyritic Basalt

Porphyritic Basalt with Plagioclase Phenocrysts

Quartz Vein in Host Rock

Silicon Dioxide (SiO2)

Pumice

Vesicular volcanic glass (Amorphous silica mixed with various oxides)

Porphyry (Rhyolite / Andesite Porphyry Pebble)

Porphyritic Igneous Rock

Rounded beach cobble, likely vesicular basalt

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

Vesicular volcanic rock, likely weathered pumice or scoria

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

Tuff

Volcanic Tuff

Snowflake Obsidian (or similar porphyritic volcanic rock)

Obsidian with Spherulites (if glassy), or Porphyritic Rhyolite/Andesite (if crystalline groundmass)

Obsidian (likely black volcanic glass)

Obsidian; naturally occurring rhyolitic glass, primarily SiO₂

Tumbled amethyst

Amethyst, purple variety of quartz (SiO₂)

Polished dark stone, possibly obsidian

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

Basalt

Extrusive Igneous Rock

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

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

Fine-grained gray rock, likely andesite or basalt

Aphanitic volcanic rock; probable basaltic-andesite (plagioclase ± pyroxene, minor iron oxides)

Olivine Basalt (Pumice or Scoria)

Mafic extrusive igneous rock

Dark volcanic sand / basaltic sand

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

Basalt

Extrusive Igneous Rock

Basalt

Extrusive igneous rock

Basalt

Extrusive Igneous Rock