Groundwater traveling through limestone beds dissolves calcium carbonate, an environmentally sensitive process that depends on a delicate balance between temperature, water chemistry and carbon dioxide levels in the air. As the mineral-saturated water encounters surface conditions, this dissolved matter precipitates in thin layers of calcite or aragonite, two crystallographically different forms of calcium carbonate (CaCO3). With time, the minerals build up into deposits of travertine.
The region around Rome produces large travertine deposits that have been exploited for thousands of years. The stone is generally solid but has pore spaces and fossils that give the stone character (see an example of travertine building stone in the Limestone Picture Gallery). The name travertine comes from the ancient deposits on the Tibur River, hence lapis tiburtino. See more photos and learn more detail in the Travertine Picture Gallery.
"Travertine" is sometimes used to mean cavestone, the calcium carbonate rock that makes up stalactites and other cave formations.
For more photos see the Sedimentary Rocks Gallery.
Other galleries:
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society
