Agate is a banded variety of chalcedony that occurs as translucent to opaque. The beautiful patterns shown in polished agate were caused when microscopic crystals formed in bands and coloured deposits filtered through cavities in porous rocks.
Agates are usually dyed to create exquisite banded varieties of blues, oranges, greens and many other shades. The more densely packed layers of crystal in the agate slabs resist dye and so remain white, whereas the softer layers prove more porous to the dye and so shade in accordance with the density of the crystals. The Egyptians used agate in jewellery 3,000 years ago. Today, agate is used in a number of ways due to its toughness. Agate can be seen in jewellery, objets d’art, beads, flatware and in cameos.
The name is said to derive from the River Achates (now called the Drillo) in Sicily as the gemstone was frequently found there. Today, the main agate deposits are Brazil, Uruguay, Australia, China, India, Madagascar, Mexico, Mongolia, Namibia and the USA.