Figure 3: Background on fission tracks and examples of fission track etching. (a) Schematic illustration of a fission track. (b–d) Transmitted light photomicrographs of experimentally etched fission tracks in natural glasses (b), naturally etched fission tracks in minerals (c) (i.e., revealed by fluid alteration along a fracture in monazite (left) or by weathering and corrosion around the outer surface of a sphene grain (right)), and fission tracks in synthetic borosilicate glass (simulated nuclear waste glass) etched only with deionized water (d). (e) Scale comparison (1 : 1) of an experimentally etched fission track in natural moldavite glass (top), with two “naturally etched” fission tracks in submarine volcanic glass (sample DSDP-418A-75-3[120–123]; see close-ups and petrographic context of these two fission track etch-tunnels in Figures 11 and 13).