Nanostructure of palygorskite/sepiolite in Texas caliche: Possible bacterial origin

In a caliche from west Texas, watermelon-shaped calcite crystals are coated with fibers of palygorskite/sepiolite clay, which also extend out into pore spaces as spiky filaments. Some filaments are smooth and capped by ovoid 30 - 100nm beads. Other filaments are made of rosary-like chains of beads. These objects are seen both in gold-coated and carbon-coated samples, thus are not artifacts. We suggest that these minute features were cells of nannobacteria (dwarf forms) that precipitated the clay filaments, in a similar manner as larger bacteria that accumulate clay minerals on their negatively-charged cell walls.