Tuff is a type of rock that generally consists of compacted volcanic ash or dust that was ejected during volcanic eruptions. Since volcanic activity has taken place throughout history and continues even today, the age of tuffs may vary drastically.

Due to the wide variance of characteristics that are associated with tuffs, the rocks are often classified in a number of ways in order to more specifically identify the material. Tuffs may, for instance, be described as crystal, lithic, or vitric, depending on the general nature of the material of which they are primarily comprised. The rocks are also sometimes described more specifically based upon the type of lava from which they formed or a specific substance which dominates their makeup. Among the most common of the tuffs is a reddish-brown andesitic tuff, which can be found along the Cordilleras and Andes mountain chains as well as in Japan, New Zealand, the West Indies, and a number of other locales.

Typically soft and porous, tuff was often an ingredient found in the early type of concrete developed by the Romans. Some types of the rock, such as the trachyte tuff known as peperino, were also utilized in Rome as individual building stones. In other areas, a pumiceous tuff commonly referred to trass has been utilized to a great extent as a hydraulic mortar. Nevertheless, during modern times in most parts of the world tuffs are of little economic consequence.

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