Felsite

Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition.

This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite.

In some cases, it is sufficiently fine-grained for use in making stone tools.

Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture.

Dendritic manganese oxides such as pyrolusite or iron oxides such as limonite may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.