Identify any rockfrom a photo.

Vesicular volcanic rock (likely pumice or scoria)

Gas-rich volcanic lava; likely pumice (silica-rich) or scoria (iron-rich)

Rounded pebble, likely quartzite

Quartzite (dominantly recrystallized quartz, SiO₂); identification is uncertain from the image alone

Rounded river pebble

Unidentified lithic pebble; exact rock type cannot be determined from the image

Light-colored rounded pebble, likely quartzite

Quartzite, composed predominantly of recrystallized quartz (SiO₂)

White quartz pebble

Quartz (SiO₂), likely massive milky quartz

Milky quartz pebble

Quartz (silicon dioxide, SiO₂)

Rounded river pebble (lithology unclear)

Indeterminate natural rock; no specific mineral or rock type can be identified from the image

Pumice

Pumice, a highly vesicular volcanic rock composed mainly of rhyolitic or dacitic glass

Botryoidal chalcedony (white agate)

Microcrystalline quartz, SiO₂ (chalcedony)

Botryoidal chalcedony (likely common opal)

Silica, SiO₂; chalcedony is microcrystalline quartz, while opal is hydrated amorphous silica (SiO₂·nH₂O)

Likely gray shale or mudstone

Fine-grained siliciclastic sedimentary rock, composed mainly of clay minerals and quartz; exact identification is uncertain from the image.

Weathered granite

Granite, chiefly quartz and feldspar with dark mica or amphibole