Agates have been discovered in numerous countries all over the world. In fact, it would be difficult to identify a country on the map that does not possess a single commercial source of this stone. The numerous sources of agate can be explained by the key ingredients that form this stone. This stone largely contains SiO2 or silica. Given that silicon dioxide is the most common mineral on the crust of the earth, the abundance of agates is expected. In geological history, i.e. several million years ago, water dissolved silica in rock formations and volcanic ash on the surface of the earth.
Slowly, the water evaporated and the dissolved SiO2 was left behind as a solid residue. Under geologic conditions of high pressure and temperature the salt was hardened and was converted to stones that we find today. The main reason that gives agates their usual patterns is that the silica was deposited in well-defined layers. Each layer contained a unique set of secondary minerals, some of which changed the appearance of the primary mineral – silica. In other cases, the inorganic solution had organic materials such as branches. As millions of years passed, the organic matter decomposed to be replaced with other minerals, leading to the formation of petrified wood. Agates commonly have a hardness rating just over 7 on the Mohs scale. The unit weight as compared to that of water of agates varies between 2.6 and 2.7.