Identify any rockfrom a photo.

Weathered granite or granitic rock

Granite; chiefly quartz, feldspar, and mica

Weathered quartz-rich pebble

Likely quartzite or quartz-rich granite/granitoid; exact identification requires testing

Weathered quartz-rich river pebble

Likely altered granite or granitic gneiss, composed mainly of quartz, feldspar, and minor mica/iron oxides

Tumbled quartz-rich river pebble, possibly quartzite

Quartzite (predominantly SiO₂), or quartz-rich siliceous rock

Rounded river pebble, likely quartz-rich sandstone or quartzite

Indeterminate; probable quartz (SiO₂) with feldspar, iron-oxide staining, and minor lithic grains

Rounded quartz-rich cobble, likely quartzite or weathered granite

Quartzite (mostly SiO₂), possibly feldspathic quartzite; exact identification requires testing

Rounded sandstone pebble

Quartz-rich sandstone, likely arkosic or lithic sandstone

Rounded quartz-rich sandstone or quartzite cobble

Quartz-dominated siliciclastic rock; likely sandstone, possibly weakly metamorphosed quartzite

Rounded basalt cobble

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

Rounded basalt cobble

Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine

Rounded basalt cobble

Basalt; fine-grained mafic volcanic rock, commonly containing plagioclase, pyroxene, and olivine

Rounded iron-rich river pebble

Likely ferruginous sandstone or ironstone; exact identification requires testing