The name of this stone comes from the Greek name of the river, which is on the island of Sicily, – Achates (today known as Dirillo). Agate was found in this area even in the time of Theophrastus. There is also a suggestion of an earlier – Semitic – origin of the name, from the Arabic word «aqiq», which means “hair of a newborn baby”. And Aqiq is also the name of valley near Medina.
Formation of agate and features of the structure
Agate is formed in hydrothermal veins or in the cavities of volcanic rocks. It can also be found in petrified wood. Minerals the structure of which is formed from microcrystalline quartz and hydrated silica refer to chalcedony. Agate is also included in this group. Agate can be characterized by a layered structure, showing the shape of the cavity in which the mineral was formed. Layered texture of agate is represented by multiple layers, each of which is unevenly transparent and has its hue.
This stone may have banded texture (color in the form of bands of irregular shape). This feature for a long time remained a subject of debate. One of the assumptions based on the fact that silicon solutions, which make up the agate, are formed either in the final stages of magmatic activity, or during subsequent weathering. This banding can be so thin that 2.5 cm of the material there can be up to 20 thousands of individual micro-fibers (for example, this happens in iridescent agate). Thus, the strip is seen as a result of rhythmic crystallization in gel. Another suggestion offered by German chemist R. Liesegang, that is the bands of agate are equated with “Liesegang rings”. 
The theory is that the “rings” are formed as a result of periodic deposition of substances from reacting solutions in gel media. Silica gels filled micro-cameras in the structure of agate. They “matured” there and then divided into concentric layers, and came to the stage of crystallization.
As you can see, the most attractive feature of the agate texture is a very complex question, but it is such decorative feature thanks to which the stone is very beautiful and unique. Alternation of gray-blue and white layers is typical for the most expensive agates of emerald or pink colors.
Coloring of agate
There are many types of agate. For example, moss agate is characterized by the inclusion of various fibrous materials or manganese oxides, in this regard, on the polished surface of the stone (for example, ruin agate or fortification agate) decorative patterns could be seen. 
There is the so-called bastion agate. Its texture feature is that due to the intersection of the individual layers unique patterns are formed. These patterns look like cityscapes or bastions. The pattern of thin concentric layers is typical for Brazilian agate. There is also ocellar agate. Its texture is represented by bars around one central point. There are examples of such an agate with rock crystal lens in the center. These stones are very valuable. Blue agate usually has a so-called sapphirine or light blue coloring. Iridescent agates are of great value too. Such agates have optical effect of the iridescent color shine. For black agate brown, gray or other colors with dark shades are quite typical. Jewelry with black agate was presented in one of the collections of Oscar De La Renta.
Deposits of agate
Agate is mined in the Urals, in Georgia (Akhaltsikhe), Tajikistan (Adrasman), Brazil (Minas Gerais), Armenia (Idjevan), India (Deccan Plateau). Also large deposits can be found in Mongolia and Uruguay.
Application of agate
Besides that agate is of great demand in the jewelry business, in the manufacture of various decorative items and accessories, this stone has been used in a very unusual way. For example, there is a curious fact that agate was used for the manufacture of umbrella handles for a long time. For this purpose they were often stained, but the numerous bands of agate absorbed the dye in different ways (for example, white puffs absorbed dye badly). It is known that artificial coloring of agates gives material suitable for making cameos. In laboratories agate can be used for manufacturing of the reference precise weight prisms, or in the manufacture of grinding powders. More often stones for clocks were produced from agate.
It is known that in the XIX century such cities as Idar and Oberstein on the Noe River were famous for their workshops in which cutting and polishing of agate stones were skillfully performed. Today some factories survived, where craftsmen demonstrate vintage art turning and polishing of agate. For this they use a large vertical wheel of sandstone, which is rotated by falling water.
Agate is also suitable for carving. The world’s largest product of agate is represented in one of Vienna’s museums. It is a flat dish with a diameter of 75 cm, which was carved out of solid rock. It is also known that agate was used to create the Florentine mosaic “kommesso”. Its peculiarity is that the masters put specially cut pieces of semi-precious stones in artistic compositions. This technique was invented in the XVI century, in Florence. In addition to agates, to create mosaics they also used jasper, chalcedony, granite, porphyry and quartz. These mosaics decorated luxurious countertop, small wall panels and other interior elements. The pattern in this composition could be of different symbols and colors, or it was whole landscapes with lots of details. The trend towards the use of agate in exclusive projects of interior decoration is still relevant today.