MEXICAN ONYX is a name given to a fine-grained variety of calcite formed in caves and waterfalls, and is known as travertine. The material forms in a number of different colors, and is sometimes dyed, and is carved into animals, geometric shapes and other ornamental items. Since calcite is dissolved with hydrochloric(muriatic) acid, pieces are often given their final polish by immersing them in acid.
Travertine is found in many parts of the world including the US. Massive deposits in Pakistan are also being used for cutting and carving into many beautiful objects. Click her for more information on PAKISTANI ONYX.