Igneous Rock (Volcanic Glass)

Weathered porphyritic volcanic rock, possibly rhyolite or andesite

Altered porphyritic rhyolite–andesite; likely quartz/feldspar phenocrysts in a fine volcanic groundmass

Possibly black obsidian or polished basalt

Volcanic glass (obsidian; chiefly SiO₂) or fine-grained basalt

Vesicular basalt (possibly scoria)

Basalt; chiefly plagioclase feldspar, pyroxene, and often olivine, with volcanic glass

Peridotite (Olivine-bearing Xenolith)

Peridotite (predominantly Forsterite Olivine, Mg2SiO4)

Basalt Pebble

Extrusive mafic igneous rock

Weathered mafic rock (probable basalt or gabbro fragment)

Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine

Tumbled gray pebble, likely basalt or dark chert

Most consistent with fine-grained basalt (plagioclase–pyroxene), though gray chert (microcrystalline SiO₂) is possible

Weathered vesicular volcanic rock (likely vesicular basalt or scoria)

Vesicular basalt; primarily plagioclase, pyroxene, and iron-rich oxides, with possible glass

Likely basalt (possibly weathered volcanic rock)

Basalt; predominantly plagioclase feldspar and pyroxene, with possible olivine and iron oxides

Porphyritic volcanic rock, likely andesite or basalt with weathered feldspar phenocrysts

Porphyritic andesite–basalt; chiefly plagioclase feldspar and pyroxene, with possible olivine or iron oxides

Weathered mafic rock, likely basalt

Basalt; predominantly plagioclase feldspar and pyroxene, possibly olivine and iron oxides

Basalt (likely vesicular basalt)

Basalt; primarily plagioclase feldspar, clinopyroxene, and olivine, with iron-titanium oxides

Likely weathered basalt or iron-rich volcanic rock

Basalt; primarily plagioclase feldspar, pyroxene, and iron-rich oxides

Basalt Pebble

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Basalt

Extrusive Igneous Rock

Vesicular Basalt (or Rhyolite)

Extrusive Igneous Rock with Vesicular Texture

Basalt (Polished)

Extrusive mafic igneous rock

Basalt (River Stone)

Extrusive mafic igneous rock

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

Weathered vesicular volcanic rock, likely pumice or scoria

Vesicular rhyolitic pumice or basaltic scoria; exact identification requires a clearer image and tests

Granite fragment

Granite, a coarse-grained felsic intrusive igneous rock composed mainly of quartz, feldspar, and mica

Basalt

Basalt (Igneous Volcanic)

Agate

Silicon Dioxide (Chalcedony), SiO2

Fine-grained dark gray rock, likely basalt

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

Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Pumice

Vesicular Rhyolite or Dacite

Rounded dark mafic cobble, likely basalt

Basalt; primarily plagioclase feldspar, clinopyroxene, and commonly olivine or magnetite

Vesicular basalt (likely scoriaceous basalt)

Basalt; chiefly plagioclase feldspar, clinopyroxene, olivine, and volcanic glass

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Basalt (River Stone)

Extrusive mafic igneous rock

River Stone (Basalt)

Extrusive Igneous Rock (Mafic)

Iron-rich volcanic rock, possibly hematite-bearing basalt

Basalt with iron oxides/hydroxides, chiefly hematite (Fe₂O₃) and possibly magnetite (Fe₃O₄)

Weathered dark-gray pebble

Likely basalt or a basaltic volcanic rock; exact identification requires testing

Porphyritic Igneous Rock / Rhyolite Porphyry

Porphyritic volcanic rock

Brecciated jasper (likely ocean jasper or rhyolitic jasper)

Silica-rich volcanic breccia composed mainly of microcrystalline quartz/chalcedony (SiO₂), with iron-oxide staining and possible feldspar

Basalt pebble

Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine

Rounded basalt cobble

Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, with minor olivine and iron oxides

Iron-rich volcanic rock fragment (likely basalt or weathered scoria)

Basaltic rock; primarily plagioclase feldspar, pyroxene, and iron oxides

Vesicular basalt

Basalt, chiefly plagioclase, pyroxene, and olivine

Dark gray basalt or andesite cobble

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase feldspar, pyroxene, and possibly olivine