This gemstone has been prized since antiquity and is a variety of Chalcedony, which in turn is a member of the Quartz family.
It was given its name by Theophrastus, a Greek philosopher who is believed to have discovered the gem on the banks of the river Achates in the 4th century BC. The gemstone was later mentioned in the Bible as one of the “stones of fire”.
Made from silicon dioxide, it has a glassy (vitreous) lustre, and registers 7 in hardness on the Mohs scale. Being such a hard stone, Agate is often used to make brooches and pins. Additionally, as it can also resist acids (unlike a lot of other gemstones) it has been used to make mortars and pestles to press and combine chemicals.
Many Agates originate in cavities of molten rock, where gas bubbles trapped in solidifying lava are replaced with alkali and silica bearing solutions. Formed as a banded round nodule (similar to the rings of a tree trunk) the gem boasts an exquisite assortment of shapes and colours of bands, which may be seen clearly if a lapidarist cuts the sections at a right angle to the layers: this is sometimes referred to as Riband Agate.
Other types of Agate include Onyx (Onyx is almost always a dyed Agate), Sardonyx, Ring Agate (encompassing bands of different colours), Moss Agate (with green banding), Blue Lace Agate, Turritella Agate, Snake Skin Agate, Rainbow Agate and Fire Agate.
Myths and legends suggest that when a person wears Agate, they become more pleasant and agreeable. It is believed to quench thirst, protect against viruses (including fever) and to cure insomnia. Some tribes in Brazil also believe that Agate can even cure the stings of scorpions and bites from poisonous snakes. Cut off from society often without modern medicines Agate is used for a variety of ailments.
Muslims often have the gem set into a ring and wear it on their right hand and have the name of Allah, Ali, or one of the names of the other eleven Imams inscribed on the ring.
The gem can be found all over the world, but the main sources of gem-quality material come from Rio Grande do Sul in Brazil. It can also be found in the United States - in particular the west; Montana and Idaho - Australia, Italy, and also a very small supply from Madagascar.