If you happen to search for agates at extreme low tide in the Usan area, you may uncover very weathered material, characterised by strongly white colouration at the edges of the nodule. I have been lucky enough to find one large piece (both halves of which are photographed on other pages) of close to 8cm in diameter with what amounts to extremely washed-out and highly-altered colouration and banding. Often constant immersion in seawater and sand causes orange, red, grey-blue or otherwise colouring to appear dark grey or black on the outside of a nodule. Generally, once cut these specimens display none of the darker pigmentation showing on the exterior, although happily, and only occasionally, sometimes the rich colour has seeped through. Every so often pieces occur that were once clearly all agate, however now have been weathered until the stone itself has begun to dissolve, and where this has occurred none of the original pattern is visible. Another 8cm nodule  I collected in the Usan area displayed an almost completely unpolishable centre, albeit with lovely, and highly intricate banding still extant along the edges.