Welded tuff/volcanic breccia

Volcanic breccia

Volcanic breccia or welded tuff

This is an example of a welded tuff. Angular chunks of ryholitic lava are "glued" together by a darker mafic lava. This is probably a debris fall from a massive volcanic explosive eruption. The lava that glued the fragments together was still molten at the time that the rock formed.
This sample came from a Colorado River terrace gravel deposit near Lake Havasu City, Arizona.
https://gotbooks.miracosta.edu/rocks/igneous/29.html 2/2/2021