Cast of a woody angiosperm
Java, Indonesia

A cast provides a record of a fossil structure that has been completely replaced. In this instance, a branch rotted away in the matrix in which it was buried, allowing the cavity to be filled later with a variety of minerals. Among these were iron oxides or iron-oxide-containing minerals that formed dendritic patterns similar to those seen in plume and moss agates.
Copyright © 2000 Giraud Foster & Norman Barker