FIG. 3. Altered symplectic (eutectoid) grains ENSM. (a) Os-Pt-Ru iridium grain with eutectic texture. Metal residues (white) display parallel, curved and crooked lamellar shapes (Table 1, col. 1). Pol. sect. SEM(BS). 260 µm. (b) Border of the same grain, showing the residual metal (white), rimmed by incipient oxide (smooth grey), embedded in an oxidic matrix (fibrous grey), and a border of well-developed Ir-oxide crystals (light grey). The nearly complete disappearance of the metal in the border layer is notable. SEM(BS). 65 µm. (c) Border of the particle, showing the local development of larger fibrous/tabular Ir-oxide crystals. (Table 1, col. 2). SEM(BS). 10 µm. (d) Another field of the same border under RLM, showing the large difference in reflectance of the crystals and the metal. 12 µm.