No gemstone is more creatively striped by nature than agate, chalcedony quartz that forms in concentric layers in a wide variety of colors and textures. Each individual agate forms by filling a cavity in host rock. As a result, agate often is found as a round nodule, with concentric bands like the rings of a tree trunk. The bands sometimes look like eyes, sometimes-fanciful scallops, or even a landscape with dendrite trees.

Agate was highly valued as a talisman or amulet in ancient times. It was said to quench thirst and protect from fevers. Persian magicians used agate to divert storms. A famous collection of two to four thousand agate bowls, which was accumulated by Mithradates, king of Pontus, shows the enthusiasm with which agate was regarded. Agate bowls were also popular in the Byzantine Empire. Collecting agate bowls became common among European royalty during the Renaissance and many museums in Europe, including the Louvre, have spectacular examples.

• Blue Lace Agate - Agate with light blue bands in a lacy or wavy pattern.
• Botswana Agate - Agate from Botswana banded with fine, parallel lines, often with a preponderance of pink blending into white.
• Brecciated Agate - Agate with broken fragments naturally cemented together.
• Cloud Agate - Grayish Agate with blurry, foggy patches of inclusions.
• Crazy Lace Agate - Agate composed of twisting and turning bands of various colors.
• Dendritic Agate - Chalcedony with tree-like or fern-like inclusions.
• Enhydro Agate - Agate nodule partly filled with water. The water can be seen from the outside of the nodule when held up to the light. Also known as Enhydritic Agate.
• Eye Agate - Agate with banded, concentric rings.
• Fairburn Agate - Beautiful, unique, and rare Fortification Agate from Fairburn, South Dakota.
• Fire Agate - Agate with Goethite or Limonite inclusions, which cause the stone to be iridescent.
• Fortification Agate - Agate with a pattern resembling a medieval fortress (i.e. imaginary moat and castle walls can be perceived).
• Fossil Agate - Agate as a replacement of organic material.
• Iris Agate - Iridescent Agate exhibiting all colors of the spectrum when sliced in thin slabs.
• Laguna Agate - Beautiful and colorful type of Agate from Ojo Laguna, Chihuahua, Mexico.
• Landscape Agate - Chalcedony with tree-like designs closely resembling scenery.
• Mexican Lace Agate - Agate consisting of thin bands in a lacy or wavy pattern.
• Moss Agate - Chalcedony with dense inclusions of green Hornblende.
• Nipomo Agate - Agate with Marcasite inclusions found in Nipomo, California.
• Onyx - Agate where the banding lines are straight and parallel, and consistent in band size.
• Oregon Snakeskin Agate - White to cream Chalcedony with a wrinkled or cracked "skin", found in Oregon.
• Plume Agate - Agate with inclusions in feather-like patterns.
• Pom Pom Agate - Agate with yellow inclusions resembling pom poms.
• Pseudo Agate - Agate as a replacement of organic material.
• Rainbow Agate - Iridescent Agate exhibiting all colors of the spectrum when sliced in thin slabs.
• Sardonyx - Agate with straight parallel bands of brownish to red alternating with white or black bands.
• Sagenite Agate - Clear Chalcedony containing inclusions of other minerals.
• Scenic Agate - Chalcedony with tree-like designs closely resembling scenery.
• Snakeskin Agate - Reddish brown Agate with black concentric bands.
• Star Agate - Agate with banding lines in the formation of a star.
• Sweetwater Agate - Chalcedony with star-shaped patterns of manganese oxide inclusions, found in the Sweetwater River, Wyoming.
• Thunder Egg - Nodule filled with Agate in the center.
• Tube Agate - Agate with tube-like formations which are sometimes hollow

Literally hundreds of Agate types were coined with special variety names. Most of these are hardly known, and new ones are made up every year. Most of these names have no scientific support, and it is not in the scope of this guide to list all variety names. The list below cites only the well-known and commonly used variety names.

Care of Agate:  Agate will chip and crack rather easily though it has a hardness rating of 7. 

Enhancements: Since agate is porous, it is often dyed to enhance its natural color. Often treated agate is sold as Black Onyx. 

Bibliography: 

• The curious lore of precious stones - Author Kunz, George Frederick, 1856-1932.
• Gem identification made easy - Matlins, Antoinette Leonard.
• Gems: Their Sources, Descriptions and Identification - By Robert Webster, Peter G. Read (Editor).
• Gemstone Enhancement: history, science and state of the art - by Kurt Nassau.
• Gemstones of the world - Walter Schumann ; translated by Evelyne Stern.

A Disclaimer:  Effort has been made of including information that is found in at least two sources. I can make no claim on the accuracy of this information. I am not a Geologist or Gemologist. I make no guarantees and infer no warranties. For more information, please refer to the bibliography.

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Copyright Information.:  Although I have included a bibliography, but no attempt has been made to give credit to individual passages. If you are an author and feel that I have infringed on your copyrighted material please let me know. With that in mind, all material and information, retain their respected Copyrights.

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I encourage the reader to pursue the further study of any topic that they find particularly interesting. A good place to start is your local library.