Issues

Agates (a) Specimen ‘Maddina 3’ showing a contrasting lighter colouredwall contact layer and vertical cracks. (b) The same slab of ‘Maddina 3’ in thin section demonstrating the sweeping chalcedonic fibrosity that runsmostly from the outer edge to the centre of the agate. (c) Specimen ‘Botswana 112’ – an unusual agate showing a clean fracture between the brown region and the black and white centre. The fracture is shown on the extreme right and insert. (d) A thin section of the same agate showing a less pronounced fibrosity than in ‘Maddina 3’. The insert shows the contrasting microtexture of thewall contact band against the lighter texture of the bulk of the agate. Figs (b) and (d)with crossed polars; scale bars for the whole agates = 1 cm; Fig (c) insert = 5 mm; Fig. (d) insert = 1 mm. See Moxon (this issue).