High-resolution TEM imaging consistently identified platy layers of partially crystalline material infilling the tubules. The lattice spacings and diffraction patterns showed that this material comprises a mix of two-layer and three-layer silicates. Closer inspection of the contact point between the tubules and the surrounding basalt glass commonly revealed a thin leached rim around the tubules. Electron energy loss spectroscopy mapping demonstrated that these rims are depleted in everything but Si and O, which implies that they are formed by a leaching process, likely the incongruent dissolution of the glass during formation of the tubule. The infilling material is depleted in Ca and enriched in K, and in most cases also enriched in Fe, which is consistent with their identification as Fe-bearing phyllosilicates. These observations are consistent across the samples, which implies that the processes that form and mineralize tubular glass alteration features are similar throughout the oceanic subsurface and through time.
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