Travertine stone deposits are found across the world from the USA in the hot springs of Yellowstone National Park to the cascading asymmetric folds and cliffs of the travertine terraces 30km North of Nyalam in southern Tibet, but much of the best travertine is quarried and exported from around the Mediterranean, particularly from Italy and Turkey.

This fascinating substance is created in a similar process of deposition of minerals from water that forms stalactites and stalagmites but is associated with riverbeds, hot springs, and other sources of subterranean water. It is a form of heavily compacted limestone much denser than limestone but not as dense as marble. All these rocks are a form of Calcium Carbonate, CaCO3, and the classification of travertine depends not only on the form of CaCO3 but also on the amount of it present in the rock relative to other minerals and impurities.

Two elements of the content and structure of the rock determine the variety and range of travertine. Firstly travertine has an aero-sponge structure, in other words the rock contains small holes and fissures. These are formed by gas trapped during the formation of the rock and through the degradation over time of impurities in the rock. The density, size and character of these holes and fissures varies across a categorisation of travertine that is broadly based on a regional or quarry based classification. In most modern uses travertine is filled with a resin compound giving a dense, durable and smooth surface where the holes and fissures become part of the pattern of the surface of the stone. Secondly, trace impurities within the travertine generally of minerals, such as iron, or of organic compounds create swirls and shapes and intricate patterns in a palette that includes soft and deep dark orange, honey colours, black, white, greys, and reds.

Although travertine can be brought to a highly polished finish and is even used as a gemstone, for example Mexican onyx, it is not usually finished this way when used in the home and instead it is first filled, then honed, i.e. brought to a very smooth silk-matt finish, and then sealed with a protective matt stone sealer.

Travertine is a naturally occuring depository rock and as such can occasionally be found filled to a greater or lesser extent with fossils, typically ammonites.