Travertine is a sedimentary rock which is formed by the transformation of limestone. Carbon dioxide rich water passes through limestone, dissolves it and becomes saturated in it. Changes in temperature and pressure occur and the carbon dioxide is released into the atmosphere as it reaches the surface of the earth. As carbon dioxide is released at these hot springs, the limestone loses its ability to remain in solution and recrystallises over up which is the travertine we see today.
Its main constituents, Calcite and Gypsum, are colourless however minor impurities, other compounds and organic pigments give it common mellow hues of gold, brown and yellow.
Visually travertine will have a holy appearance which can vary from tiny pinholes to large irregular voids. This is due to the presence of gas bubbles when it is formed. Once the travertine is cut into tiles, the holes can either be filled with grout or epoxy fillers or left unfilled.