There are many kinds of agates with different pigment, impurities and various shapes and patterns. Agates can be divided into opaque, translucent and transparent varieties. Colors can be red, blue, green, light-green, tan, brown, purple, black or other hues. Agates can be layered or not, or display patterns, and some have an oily or glassy sheen.

If categorized by shape, agates can be differentiated as Onyx (including the Sardonyx), Red Onyx, Moss Agate (including the Dendritic Agate), Moonstone, Fire Agate and Agate with Water.

In Chinese history, there are references to the Agate Urn in the emperor period and Red Jade before the Eastern Han Dynasty (25-220). The name for agate is derived from the Sutra following the Eastern Han Dynasty, when agates, especially Red Agate, were held in high regard. One antique store has posted a sign that says whoever has an agate with no red coloring will be poor forever.

People in ancient China described the agate as the brain of horse for its resemblance in color and shape to the brain of a horse. But the word agate originated from the Sutra and then was relayed to China according to Zhang Hongzhao, a famous gemologist and the father of geology in modern China. In Sanskrit, asmargarbha means agate.

But in the Tang Dynasty (618-907), an eminent monk named Hui Lin explained that “asmar means horse, and garbha means brain.” Coincidentally, Cao Pi, the emperor of the Wei Dynasty (220-265) said in his book The Poetry of Horse’s Brain: “Agate belongs to jade and was originated from the Western Region. It has a crossing veins and looks like the brain of horse, so people named it horse brain.”

During the Tang Dynasty (618-907) Chen Zangqi said in his book Ben Cao Shi Yi: “The red color of agate is just like the brain of horse.” Barbarians used to say that agate was spit out by horses. So it’s no wonder that in the documents and materials before the Eastern Han Dynasty (25-220), you can’t find the word agate, even in the most authoritative dictionary, Shuo Wen Jie Zi, written by Xu Shen.