This project is to continue work on the genesis of repetitive, associated self-organization patterns of texture and composition of quartz in volcanic agates. The main patterns to be studied are (a) the systematic interlayering of bands made up of twisted (and very fine and high-Al) chalcedony fibers with bands made up of non twisted (and coarser and low-Al) fibers, and (b) the systematic association of fibrosity with banding, and of non-fibrosity with lack of banding. We theorize the fibrous habit and texture are produced by a morphological instability of the crystallization front. This spatial instability causes the front autonomously to develop regularly spaced fingers, each of which becomes a quartz fiber. The fibers produced by the morphological instability pierce through decreasing Al contours produced by another instability (an autocatalytic one, which is temporal), and grow by accretion of conical "sleeves," their rims being forced to incorporate more Al than their centers. This causes the fibers to grow twisted. This project will unravel the dynamics of agate crystallization -- a complex self-organization process with geochemical, crystallochemical, and petrologic significance well beyond agates. It will clarify also the geochemical factors that control crystal morphology and authigenic-texture type in other minerals and other low-temperature environments.
