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Unusual sponge-like texture on silica rocks. (A) Elizabeth Mahon has prominent digitate structures that appear smooth compared with sponge-like texture of the lower portions (MI mosaic, sol 1157, P2976). (B) A piece of sinter from the rim of the extinct Roosevelt Hot Spring shown in Fig. 5 has a remarkably similar texture, likely due to corrosion from late-stage fumarolic activity.
