Onyx is a banded variety of chalcedony. The colors of its bands range from white to almost every color. Commonly, specimens of onyx contain bands of colors of white, tan, and brown.
Onyx is formed of bands of chalcedony in alternating colors. It is cryptocrystalline, consisting of fine intergrowths of the silica minerals quartz and moganite. Its bands are parallel to one another, as opposed to the more chaotic banding that often occurs in agates.
Black onyx is perhaps the most famous variety, but is not as common as onyx with colored bands. Artificial treatments have been used since ancient times to produce both the black color in Onyx also comes in a greenish-white color and has obvious layers, though they do not alternate colors and are not perfectly parallel. It is translucent and almost “soft” in texture.
Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items.
Travertine is a form of limestone formed by mineral springs, especially hot springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, and cream-colored varieties. It is formed by a process of rapid precipitation of calcium carbonate, often at the mouth of a hot spring or in a limestone cave. In the latter, it can form stalactites, stalagmites. It is frequently used in most of the countries as a building material. Travertine is a terrestrial sedimentary rock, formed by the precipitation of carbonate minerals from solution in ground and surface waters, and/or geothermal heated hot-springs.