Identify any rockfrom a photo.

Banded iron formation fragment

Banded iron formation (BIF), composed mainly of hematite/magnetite and chert (SiO₂)

Banded gneiss cobble

Gneiss, commonly quartz–feldspar–mica gneiss

Yellow chalcedony (likely citrine-colored quartz)

Microcrystalline quartz, SiO₂ (chalcedony); yellow color likely from iron impurities

Tumbled prehnite

Prehnite, Ca₂Al(AlSi₃O₁₀)(OH)₂

Milky quartz (rough quartz crystal)

Quartz, silicon dioxide (SiO₂)

Red coral earrings

Corallium rubrum or related precious coral (calcareous coral skeleton; primarily aragonite, CaCO₃)

Banded agate (likely fire agate)

Microcrystalline quartz, SiO₂, commonly chalcedony with iron-oxide inclusions

Cut diamond tennis-chain jewelry

Diamond, crystalline carbon (C), cubic crystal system

Yellow chalcedony cabochon ring

Microcrystalline quartz (SiO₂), likely yellow chalcedony or dyed/treated chalcedony

Flint or chert, likely iron-stained

Microcrystalline quartz (SiO₂), commonly called flint when dark and nodular

Iron-rich jasper with quartz/chalcedony

Jasper (microcrystalline SiO₂), locally hematite/goethite-bearing

Flint (chert), likely chalcedony-rich variety

Microcrystalline quartz, SiO₂; flint is a dense cryptocrystalline form of chert