In a caliche from west Texas, watermelon-shaped calcite crystals arc.coated with fibers of palygorskite/sepiolite clay, which also extend out into pore spaces as spiky filaments. Some filaments arc smooth and capped by ovoid 30 -1OOnm beads. Other filaments arc made of rosary-like chains of beads. These objcets arc seen both in gold-coated and carbon-coated samples, thus are not artifacts. Wc 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.