One prevailing theory is that the the plume-like inclusions in Texas Agates result from metallic compounds infiltrating the Agate while will it is still in a gel state (think Jell-o). Differing colors result in different color plumes, including Black, Red, Yellow and White. For some reason, it seems that red plumes typically occur together with black plumes. That is to say that a stone with only black plumes is not too unusual, but a stone with only red plumes seems to be especially rare.
Very fine Plume Agates will have very distinct 'plumes' in a contrasting color Agate. More commonly (at least in Brewster Co. Agates), the plumes tend to be quite dense. And, a popular approach to working Texas Plume Agates is to slice them quite thin (as thin as one mm) to allow the plume to be seen distinctly. A clear quartz top is then added, and the entire assembly polished en-cabochon. Displays of thin-sliced and back-lit Texas Plume Agates are sometimes shown at Gem and Mineral Shows, and can provide a breath-taking view of their wondrous beauty.
