Figure F21. Photomicrograph of Sample 187-1155B-2R-1, 68-71 cm (see "Site 1155 Thin Sections"), showing the intersection of calcite veins with palagonite. Silica, Fe oxyhydroxides, and Mn oxide line the edge of the calcite vein. Palagonite is altered to clay along a dendritic alteration front associated with microbial degradation. The vertical fracture within the palagonite contains Mn-Fe oxyhydroxides and silica.