It is a type of chalcedony, which, in turn, is a variety of quartz. It has been used extensively in jewelry and interior decoration for more than 3,000 years. What characterizes the agate is its colors, distributed in parallel, straight and/or curved bands. It forms in volcanic rock cavities such as basalt and it usually contains in its central portion crystals of other minerals such as calcite, siderite, goethite and zeolite or other varieties of quartz itself like rock crystal and amethyst. The outer shape reflects the shape of the rock cavity in which the agate formed.
The most common colors are red, orange, brown, white, gray and bluish gray. But the agate can be artificially colored, a process that has been used since the 19th century. The procedure varies according to the desired color and is applied after the gem has been cut. At least 90% of the agates sold in the world are dyed. Blue, green, pink or purple agates are dyeing products, but in Australia there is blue agate. The black color may be natural or not.
The largest producer in the world is Brazil. Rio Grande do Sul has been producing this gem since 1830 and from it comes the most beautiful specimens known and the highest volume of production. Agate is also extracted in Minas Gerais and Bahia, as well as in Uruguay, whose deposits are an extension of the deposits of Rio Grande do Sul.
Sapphire is the other variety of corundum famous as a gem. With the exception of the red color, which identifies the ruby, it can have any color and may be even colorless, but the most appreciated and most valuable is the blue sapphire. The colorless sapphire is called leucossafira or white sapphire and the orange is known as padmaragaya. It usually is found in the marbles, basalts, pegmatites and lampphers and may have asterism such as ruby.
Among the famous sapphires are the Black Star, 233 g in the raw state, and Stuart. Of the gemstones, the largest of all is the Indian Star, 563 carat, which is in the American Museum of Natural History in New York. The 423-carat blue sapphire was discovered in Sri Lanka, which may be the largest faceted blue sapphire in the world and the Asia Star, 330 carats, is at the Smithsonian Institution in Washington, USA. Also famous is the 135.9 carat Ruspoli sapphire.
It is mainly produced in Sri Lanka while the other major producers are Myanmar, Thailand and Vietnam. The best sapphires come from India, but the deposits are practically depleted. The great gems come from Myanmar and the largest ones from Australia.
It is one of the most valuable gems, especially blue sapphire. It is synthesized in the same way as ruby. When it is not used for making jewelry, it is used in sophisticated ballpoint pens and optical instruments. To find the best blue sapphire ring.