Travertine is vuggy and full of holes due to it’s geyser origin. Thus a cheaper stone due to it’s less stable form. Onyx is layered and usually not so vuggy due to it’s aquatic origins. Layer upon layer set down over time as a great body of water dried up.
Travertine is limestone, in a sense. It is formed by geysers, like Old Faithful, when the extremely hot underground water dissolves the underlying limestone and carries it upwards with the geyser water. When the water falls to the ground and evaporates, it leaves behind the dissolved limestone which re-hardens into stone. Like CalistogaTM or PerrierTM waters, the new stone is full of gas bubbles, which give travertine its characteristic appearance. When it is manufactured as tiles or slabs, travertine is generally filled with cement and polished or honed.
Onyx, like travertine, is the result of water dissolving existing limestone and re-depositing it as a new kind of stone, sometimes called sinter. In limestone caves, onyx is formed by drip water, as stalagmites and stalactites. It is a very soft stone, and somewhat brittle, and needs to be installed where it will not be subject to hard wear. This beautiful stone is characterized by its translucence, and can actually be backlit for striking, dramatic effects.
Marbles and granites are quarried throughout the world in the form of huge blocks, some weighing up to 20 tons. These blocks are cut into slabs that are generally 3/4″ or 1 1/4″ thick and the faces are polished to the specified finish.