[1] Agate stones are characterized by alternating bands of different colored chalcedony and sometimes include macroscopic quartz.

[5] Hollow agates can also form due to the deposition of liquid-rich silica not penetrating deep enough to fill the cavity completely.

The priming layer is often dark green, but can be modified by iron oxide resulting in a rust like appearance.

"[10] Lace agates exhibit a lace-like pattern of bands with many swirls, eyes, bends, and zigzags.

They form when dendritic structures on the surface of an agate are pushed inward with the silica gel during their formation.

[2][13] Iris agates have bands that are so microscopically fine that when thinly sliced, they cause white light to be diffracted into its spectral colors.

[9] Typically, onyx bands alternate between black and white or other light and dark colors.

[16] Crazy lace agate, typically found in Mexico, is often brightly colored with a complex pattern, demonstrating randomized distribution of contour lines and circular droplets, scattered throughout the rock.

Similarly, coral, petrified wood, porous rocks and other organic remains can also form agate.

It has been suggested that growth is not crystallographically controlled but is due to the filling-in of spaces between pre-existing crystals which have since dissolved.

Agate is one of the most common materials used in the art of hardstone carving, and has been recovered at a number of ancient sites, indicating its widespread use in the ancient world; for example, archaeological recovery at the Knossos site on Crete illustrates its role in Bronze Age Minoan culture.

[20] The ornamental use of agate was common in ancient Greece, in assorted jewelry and in the seal stones of Greek warriors.

[21] Bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation.

The decorative arts use it to make ornaments such as pins, brooches or other types of jewellery, paper knives, inkstands, marbles and seals.

Agate is also still used today for decorative displays, cabochons, beads, carvings and Intarsia art as well as face-polished and tumble-polished specimens of varying size and origin.

Making use of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe.

The sanctuary of a Presbyterian church in Yachats, Oregon, has six windows with panes made of agates collected from the local beaches.

[23] Industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish and resistance to chemical attack.

Respiratory diseases such as silicosis, and a higher incidence of tuberculosis among workers involved in the agate industry, have been studied in India and China.