Igneous Rock (Volcanic Glass)

Basalt with Xenolith

Extrusive Igneous Rock

River Pebble (Basalt or fine-grained Quartzite)

Fine-grained Mafic Rock (Volcanic Basalt)

Black obsidian

Volcanic glass (mostly rhyolitic silica glass; SiO₂-rich)

Pumice

Vesicular volcanic glass (primarily SiO2)

Quartz-bearing volcanic rock, likely vesicular basalt

Basalt with secondary quartz (SiO₂) and possible zeolite/chalcedony infill

Quartz geode or quartz-bearing rock

Quartz (SiO₂), likely in a chalcedony- or basalt-hosted cavity

Obsidian (likely black obsidian)

Volcanic glass; predominantly rhyolitic composition (approximately 70–80% SiO₂)

Basalt with Quartz Veining

Veined Basalt (composed primarily of plagioclase feldspar, pyroxene, and olivine with quartz/calcite infill)

Orbicular rhyolite (orbicular jasper-like volcanic rock)

Orbicular rhyolite; predominantly quartz, alkali feldspar, plagioclase, and volcanic glass, with concentric spherulitic growths

Snowflake Obsidian

Volcanic Glass (SiO2 with Cristobalite inclusions)

Polished dark pebble, likely basalt or chert

Basalt (mafic volcanic rock), possibly microcrystalline chert

Vesicular Basalt (Scoria)

Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene)

Pumice

Pumice (Amorphous volcanic glass)

Pumice

Pumice (Vesicular felsic extrusive igneous rock)

Scoria (vesicular basalt)

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

Scoria (vesicular volcanic rock)

Basaltic to andesitic scoria; chiefly plagioclase, pyroxene, and volcanic glass

Scoria

Vesicular basaltic scoria; chiefly plagioclase, pyroxene, olivine, and volcanic glass

Pumice

Pumice (a volcanic glass, primarily SiO2)

Pumice

Vesicular Rhyolite or Trachyte (High-silica volcanic glass)

Obsidian

Volcanic glass (Amorphous silicon dioxide)

Pumice

Highly vesicular rhyolite/dacite (Amorphous glass)

Pumice

Pumice (Highly vesicular volcanic glass)

Rounded quartz-rich river cobble (probable rhyolite/granite-derived stone)

Indeterminate felsic igneous cobble; likely quartz–feldspar aggregate with minor iron oxides

Obsidian

Amorphous Volcanic Glass (primarily SiO2)

Rhyolite

Rhyolite (High-silica volcanic rock)

Apache Tear

Obsidian (Hydrated Silica Glass)

Mahogany Obsidian

Obsidian (Volcanic Glass) with Hematite/Magnetite inclusions

Unidentified Dark Mineral or Rock

Indeterminate (Likely Silicon Dioxide or Carbon-based)

Snowflake Obsidian

Spherulitic Volcanic Glass (primarily SiO2)

Vesicular volcanic rock, likely pumice or scoriaceous basalt

Highly vesicular basaltic–andesitic volcanic rock; chiefly plagioclase, pyroxene, and volcanic glass

Rhyolite or jasper-bearing volcanic rock

Rhyolite, likely altered and silicified; red coloration may come from hematite

Rounded basalt pebble

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

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Pumice

Pumice (a highly vesicular volcanic glass)

Agate in Matrix

Silicon Dioxide (SiO2) within host rock

Obsidian (Black Obsidian)

Amorphous volcanic glass (primarily SiO2)

Weathered basalt (probable)

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

Pumice

Pumicite

Pumice

Pumice (a highly vesicular extrusive igneous rock)

Snowflake Obsidian

Volcanic glass containing Spherulite inclusions (primarily Cristobalite, SiO2)

Pumice

Pumice (Vesicular Rhyolite/Andesite)

Rhyolitic Tuff (Breccia Type)

Rhyolitic Pyroclastic Rock (Mixed Silicates including Quartz, Feldspar, and Volcanic Glass)