Identify any rockfrom a photo.

Weathered dark flint (chert) pebble

Microcrystalline quartz (SiO₂), commonly called flint or chert

Quartz-rich mineral fragment

Quartz (silicon dioxide, SiO₂), possibly milky quartz

Rounded basalt pebble

Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with minor olivine or magnetite

Tumbled yellow chalcedony (likely citrine or yellow quartz)

Quartz, SiO₂; potentially microcrystalline chalcedony

Tumbled green aventurine (probable)

Quartz aggregate, SiO₂, commonly containing fuchsite mica inclusions

Polished brown jasper

Jasper, microcrystalline quartz (SiO₂) with iron-oxide impurities

Pink-and-white quartz-rich rock, likely rose quartz or quartzite

Quartz (SiO₂), possibly rose-quartz-bearing quartzite; minor iron-oxide staining

Black polished/tumbled stone, likely basalt or black jasper

Most likely fine-grained basalt (plagioclase and pyroxene); appearance can also match microcrystalline quartz (black jasper)

Red jasper (likely brecciated jasper)

Microcrystalline quartz/chalcedony, SiO₂, colored mainly by iron oxides

Fossil brachiopod shell

Likely spiriferid or strophomenid brachiopod; calcium carbonate (primarily calcite)

Polished brecciated jasper (likely septarian or iron-rich jasper)

Microcrystalline quartz (chalcedony), SiO₂, with iron oxides and possibly calcite or other rock fragments

Tumbled chert or flint pebble

Microcrystalline quartz (SiO₂), commonly with chalcedony and minor iron oxides