Identify any rockfrom a photo.

Weathered granite cobble

Granite, typically quartz–alkali feldspar–plagioclase with biotite or hornblende

Polished orange chalcedony (likely carnelian)

Microcrystalline quartz, SiO₂; iron-stained chalcedony

Iron-stained quartz-rich rock, likely granite or pegmatite fragment

Weathered granite/pegmatite; mainly quartz (SiO₂) with feldspar and iron-oxide staining

Faceted green gemstone, likely peridot

Olivine, gem-quality forsteritic olivine: (Mg,Fe)₂SiO₄

Likely weathered quartz-bearing rock fragment

Indeterminate granitic or quartz-rich silicate rock; chiefly quartz (SiO₂), possibly feldspar

Tiger’s eye

Quartz (SiO₂) with fibrous crocidolite pseudomorphs and iron oxides

Tumbled white stone, possibly howlite or magnesite

Howlite: Ca₂B₅SiO₉(OH)₅; possible magnesite: MgCO₃

Tumbled metallic sulfide mineral specimen, likely pyrite-bearing ore

Likely pyrite (FeS₂) with associated sulfides and host rock; exact identification requires testing

Tumbled dark purple quartz, likely amethyst

Quartz (SiO₂), purple variety amethyst; possibly iron-bearing quartz with surface sparkle

Tumbled chalcedony or quartz fragment

Microcrystalline quartz, SiO₂ (probable chalcedony)

Polished red jasper

Jasper, opaque microcrystalline quartz (SiO₂) colored mainly by iron oxides

Clear quartz crystal

Quartz (silicon dioxide, SiO₂)