Igneous Rock (Volcanic Glass)

Apache Tears (Obsidian)

Volcanic Glass (SiO2 - Silicon Dioxide with impurities)

Apache Tear

Obsidian (Hydrated Silica Rich Volcanic Glass)

Apache Tear

Obsidian (Hydrated Volcanic Glass) - SiO2 (with impurities)

Quartz Vein in Basalt

Silicon Dioxide (SiO2) in Mafic Igneous Rock

Scoria

Extrusive Igneous Rock

Snowflake Obsidian (or similar porphyritic volcanic rock)

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

Vesicular volcanic rock, likely scoria

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

Scoriaceous basalt (scoria)

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

Vesicular volcanic rock, likely scoria

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

Dark volcanic sand and basalt fragment

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine

Tumbled purple jasper (likely rhyolite-derived jasper)

Microcrystalline quartz (SiO₂) with iron/manganese oxide impurities; possibly purple rhyolitic jasper

Basalt

Extrusive Igneous Rock

Basalt (probable)

Basalt; chiefly plagioclase feldspar, pyroxene, and minor olivine or magnetite

Polished black stone, likely obsidian or dark basalt

Volcanic glass (obsidian), possibly basalt; exact identification requires testing

Vesicular volcanic rock, likely scoria

Scoria; predominantly basaltic composition (plagioclase, pyroxene, olivine, and volcanic glass)

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

River Cobble (likely Metasedimentary or Basalt)

Metamorphosed Siltstone or Altered Fine-grained Igneous Rock

Basalt

Basalt (composition: Plagioclase, Pyroxene, and Olivine)

Scoria (vesicular basalt)

Vesicular basalt; chiefly plagioclase, pyroxene, and iron-rich glass/oxides

Rounded dark beach pebble, likely basalt

Fine-grained basalt, possibly andesite or dark chert

Porphyritic basaltic-andesite cobble

Fine-grained plagioclase–pyroxene volcanic rock, likely basaltic andesite

Weathered vesicular volcanic rock, likely basaltic scoria

Vesicular basalt/scoria; mainly plagioclase, pyroxene, and iron-rich glass or oxides

Vesicular basalt (possibly slag-like volcanic rock)

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

Basalt Pebble

Extrusive Igneous Rock

Vesicular volcanic rock, likely pumice

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

Mahogany Obsidian

Volcanic Glass (with inclusions of Magnetite or Hematite)

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

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

Polished porphyritic basalt (likely)

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

Quartz (Milky/Common)

Silicon Dioxide (SiO2)

Vesicular volcanic rock, likely pumice or scoriaceous rhyolite

Highly vesicular felsic volcanic rock; commonly rhyolitic pumice (composition dominated by volcanic glass, quartz, and alkali feldspar)

Basalt with Quartz/Calcite Veins

Amygdaloidal Basalt (SiO2 or CaCO3 inclusions)

Pumice

Pumice (Vesicular intermediate to felsic volcanic glass)

Porphyritic Basalt

Porphyritic Basalt with Plagioclase Phenocrysts

Basalt

Mafic extrusive igneous rock

Porphyry (Rhyolite / Andesite Porphyry Pebble)

Porphyritic Igneous Rock

Porphyritic basaltic-andesite cobble

Porphyritic andesite to basaltic andesite; plagioclase-rich volcanic rock

Basalt (Porphyritic Basalt)

Extrusive Igneous Rock

Iron-stained Milky Quartz

Silicon Dioxide (SiO2) with iron oxide inclusions

Snowflake Obsidian

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

Obsidian

Obsidian (Volcanic Glass, primarily SiO2)