2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 6
Presentation Time: 2:50 PM


FOLK, Robert L., Department of Geological Sciences, Univ of Texas, Austin, Austin, TX 78712, rlfolk@mail.utexas.edu

Precipitation of clay minerals on cell walls of “normal” bacteria (~1 µm) is now a widely accepted process. However, the idea that nannobacteria (<0.2 µm) form clay minerals has been hard to put over, despite the first hints by Lynch pre-1994. I present here more examples. (1) West Texas caliche (work with E. T. Rasbury) contains fibers of palygorskite, filaments capped by the ovoid 40-100 nm nannobacterial cells that made them. Many filaments look like rosaries made of chains of 15-30 nm bodies. (2) Mt. Etna lava flows where the basalt contacts see water (work with F. L. Lynch) shows chlorite lining pores; the chlorite shows every transition from isolated 25-40 nm bodies , to worm-like forms, to chains of cells, to chlorite sheets with “euhedral” gross aspect. The sheets are the same thickness as the cells, showing that nannobacteria are making it, not just decorating the chlorite sheets. (3) In these altered basalts honeycomb ?smectite begins as worm-like nannobacteria 25-40 nm in diameter (randomly coating a surface); these then grow ?inorganic overgrowths to form the honeycomb fabric. (4) Kaolin from several localities appears at low magnification to be made of euhedral pseudo-hexagonal sheets; but at high magnification, they show a “hamburger patty” structure made up of coalescing 40-50 nm ovoids; again, single kaolin sheets are the same thickness as the precipitating nannobacterial cells. (5) Illite from many examples shows smooth blades with sharp crystal faces (inorganic) in contrast to illite fibers with ovoid nannobacterial cells at their tips.

In all of these examples it is easy to distinguish (1) inorganically formed clay minerals having sharp euhedral crystal margins and smooth faces, versus (2) nannobacterially-precipitated clay minerals with irregular crystal margins, with beads or worms on their edges, and a hamburger-patty-like structure on the faces. Believing must come before seeing.