Dacite banded


Extrusive igneous rock
Flow-banded dacite volcanic rock from the Pinnacles Formation in San Benito County, CA. This sample came from a highly fluid lava that was stretched like taffy, and broken up and compacted as it cooled. The Pinnacles Formation is part of the greater volcanic field that formed along the San Andreas Fault system in association with the Neenach Volcanic Field south of Bakersfield as the transform fault developed and over time, carried the Pinnacles volcano and surround rock northward nearly 200 miles to its present location over about 23 million years.
https://gotbooks.miracosta.edu/rocks/igneous/39.html 2/2/2021