Biotically or abiotically precipitated calcium carbonate, from spring-fed, heated,
or ambient-temperature water. May be white and spongy, various shades of orange, tan
or gray, and ranges to dense, banded or laminated rock. Macrophytes, bryophytes, algae,
cyanobacteria and other organisms often colonize the surface of travertine and may
be preserved, to produce the porous varieties.
Neuendorf et al. 2005; http://en.wikipedia.org/wiki/Travertine; Chafetz, H.S., and
Folk, R.L., 1984, Travertine: Depositional morphology an dthe bacterially constructed
constituents: J. Sed. Petrology, v. 126, p.57-74.