The colorful bands of an agate have been analyzed by measuring the wid
th (the standard deviation) of the greyscale profiles as a function of
length. The bridge method was also used. These are common methods to
test for self-affine fractal geometry. The profiles were found to be s
elf-affine over about two decades; and Hurst exponents of 0.36 +/- 0.0
5 and 0.49 +/- 0.05 were measured.