Igneous Rock (Volcanic Glass)

Obsidian (likely black obsidian)

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

Obsidian

Volcanic Glass (High silica amorphous rock)

Orbicular rhyolite (orbicular jasper-like volcanic rock)

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

Moss Agate with Jasper

Chalcedony (SiO2 with inclusions)

Obsidian / Volcanic Glass

Obsidian (principally SiO2, usually 70% or more)

Weathered iron-rich volcanic rock

Likely basaltic andesite or altered basalt; precise identification requires testing

Obsidian (Black)

Obsidian (approx. 70–75% SiO2)

Porous vesicular volcanic rock (likely scoria)

Scoria; chiefly iron-rich volcanic glass with plagioclase, pyroxene, and/or olivine

Pumice

Pumice (Vesicular Felsic Igneous Rock)

Pumice

Vesicular Rhyolite or Dacite Pumice (Amorphous volcanic glass)

Obsidian Arrowhead

Volcanic Glass (Amorphous Silicon Dioxide)

Vesicular Basalt

Extrusive Mafic Volcanic Rock

Basalt with Quartz Veining

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

Pumice

Highly vesicular volcanic rock, typically rhyolitic to andesitic in composition

Snowflake Obsidian

Volcanic glass with Spherulite inclusions (SiO2)

Pumice

Pumice (Vesicular volcanic glass)

Pumice

Pumice (Felsic 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

Volcanic Glass (Amorphous Silicon Dioxide)

Rhyolite or jasper-bearing volcanic rock

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

Black obsidian

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

Pumice

Highly vesicular volcanic glass, typically rhyolitic to andesitic composition; mainly silicate glass with feldspar, quartz, and minor pyroxene/amphibole.

Rounded basalt pebble

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

Pumice

Vesicular Rhyolite or Trachyte (High-silica volcanic glass)

Obsidian

Volcanic Glass (Amorphous Silica)

Agate in Matrix

Silicon Dioxide (SiO2) within host rock

Pumice

Vesicular volcanic glass (primarily SiO2)

Weathered basalt (probable)

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

Polished banded obsidian

Volcanic glass, predominantly SiO₂; likely banded or mahogany obsidian

Red Scoria

Scoria (Vesicular Basalt/Andesite)

Unidentified Dark Mineral or Rock

Indeterminate (Likely Silicon Dioxide or Carbon-based)

Pumice

Pumice (Vesicular felsic extrusive igneous rock)

Pumice

Highly vesicular rhyolite/dacite (Amorphous glass)

Scoria

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

Scoria (vesicular basalt)

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

Snowflake Obsidian

Volcanic glass containing Spherulite inclusions (primarily Cristobalite, SiO2)

River Pebble (Basalt or fine-grained Quartzite)

Fine-grained Mafic Rock (Volcanic Basalt)

Pumice

Pumice (a volcanic glass, primarily SiO2)

Quartz-bearing volcanic rock, likely vesicular basalt

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

Blue Obsidian

Volcanic Glass (SiO2 with inclusions)

Basalt

Basalt

Pumice

Pumicite