Color: Banded, depends on geographic origion
Double Refraction: +.009
Agate is a form of chalcedony, easily noted by its concentric layers. Each layer of an agate can be different from another one in opacity and color. The layers vary in size, but tend to remain the same thickness throughout the stone. Sir David Brewster noted one agate that showed 17,000 different layers in an inch of space. Agates are found as nodules or geodes in siliceous volcanic rocks. The circumference of an agate can vary from a fraction of an inch to several yards. The gem is currently believed to be created by liquid silicic acid. The acid becomes trapped in pockets of a larger volcanic rock, and as it cools, creates the layers from the outside inwards.
Geographically, agate is found all over the world. It was first discovered in the river Achates, in Sicily. The name agate is believed to be from this river. Currently, agate is mined at the Rio Grande du Sol in Brazil, also in Uruguay, Scotland, India, China, the Malagasay Republic as well as Oregon, in the United States of America. Perhaps the most famous clutch of agate was in the Idar-Oberstein region of Germany. Here, agate mining and polishing has been an important industry since the mid 15th century. In the early 1800's, however, this vein dried up. Idar-Oberstein had a thriving agate industry which slackened until the Brazilian clutch was discovered by a man from Oberstein. Idar-Oberstein is still considered the best in not only agate polishing and refining, but dying as well.
In the 14th century, a form of agate polishing was being mastered in Idar-Oberstein. Thanks to large mill built upon the river, several smiths could work on polishing agate at the same time. They harvested the power of mother nature through a large waterwheel, which turned an axle. Attached to this axle were several large sandstone wheels. Each sandstone wheel was 56 in (150 cm) in diameter and varied in width from 15 to 19 inches (40-50 cm). The width of the stone allowed for two polishers to work side by side on the same stone. The smiths lay upon special benches, parallel to the ground. With the introduction of steam power, and later electricity, this process was refined to reflect the changing times. While large agates were still broken down with hammer and chisel1, a new two-wheel process was defined. The rough, just broken agates were smoothed down on a wheel of carborundum. The smith would hold the agate between his knees in order to keep the stone still. The agate was later finished on a smaller sandstone wheel. All these wheels were kept cool to prevent damaging the stone through a water cooling system that dripped water onto the stone wheel.
Finished stones were often dyed to provide a brighter hue to the stone. While the Romans knew a method of dying agate, it was not perfected until the 1820's at Idar-Oberstein. The large influx of Brazilian stones worried the smiths. Brazilian agate was distinctly more grey, more drab than the bright reds, pinks and browns of the German stones they were used to seeing. While the dying procedure is kept as a trade secret, the process would not always work completely. Since agate is comprised of multiple layers upon layers, and each layer was different in porosity and composition than the previous layers, not every layer would take the color the same. Some layers become deeply colored and very bright, whereas others with a smaller water content and less porosity would not take the color at all. Inorganic pigments are used in the dying process as organic dyes faded and tended to not be as brilliant.
Over the millennia, agate has seen a bunch of similar, and dissimilar uses as a medicine. Ancient Egyptians used agate for rings, cylinder seals and other vessels. When forged into a talisman, they believed that the wearer would be protect from lightening, thirst would be quenched as well as receiving superior oratory abilities. Pliny also thought that agate was a healing stone. He noted a difference between geographic origin, stating that agate from India was better suited for curing diseases of the eyes, where as Egyptian and Cretian agate could cure poisons and scorpion stings. Damigeron expanded this belief by writing that agate should be ground into a powder and sprinkled on the wound, or mixed into wine and drank to cure poison. He also thought if a piece of agate was held in one's mouth, thirst would be quenched, a common theme among precious stones, and cure fevers and other inflammatory diseases. In the 10th century, a doctor (I presume) named Bard wrote a treatise on medicine. In it, he discussed the powers of powdered agate, when mixed into a liquid. He, like Pliny and Damigeron thought the liquid would cure snake poison when imbibed. He also believed the mixture to produce smoother skin. He thought a talisman of agate would be able to help fight the minions of the demon world, as well as ward off lightening and venom.
1: In the modern era, the cutting of agate is done with a diamond bladed saw.
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978
The Magic of Jewels and Charms, Dr. George Frederick Kunz. J.B. Lippincott company, Philadelphia and London, 1915