Wavellite is an aluminonphosphate (Al3(PO4)2(OH,F)3*5H2O) discovered in 1805 by Willaim Wavell (apparently in those days you could name a mineral for yourself). In this example form Arkansas, thin crystals growing radially from common nucleation points form spherical bundles of crystals. On the lower right, some of these bundles have been broken revealing the radial structure. The individual crystals are zoned in Fe concentration (showing a variation in color from one end to the other) producing the bands in color. The individual crystals are about 2mm long.
John Christensen