Opal - The Color Changing Stone
Opal: Introduction
Also known as the October Birthstone and the 14th and 18th anniversary stone, the opal is one of nature's greatest splendors. The colors can vary in any color of the rainbow. The most striking quality of opal is its ability to refract and reflect specific wavelengths of light. The interplay of different wavelengths of light gives opal its unique visual appeal and makes it one of the most sought-after gemstones in the world. It is definitely one of the world's most beautiful and precious gemstone. The word opal derives from various languages: in Sanskrit upala, meaning "precious stone", in Latin, the opalus and Greek opallios, both meaning "to see the color change".
Opal: History
The earliest known opal artifacts were discovered back from 4000 BC in Ethiopia. These artifacts were discovered later in a cave in Kenya by a famous archeologist, Louis Leakey. Opal was stated to have magical qualities and also to aid its wearer in seeing unlimited possibilities. It was also thought to loosen inhibitions and promote impulsiveness. Opal has been said in medieval times to be a cure for diseases of the eye. Opal is also stated to be a cure for blood disorders, depression, apathy, helpful with reproductive organs, filter red, and white corpuscles, and brain disorders.
Opals: How are they formed?
Opal is formed from silica-bearing waters and can be found inside any type of rock. Opal is formed from a solution of silicon dioxide and water (SiO2 + nH2O). As water runs down through the earth, it picks up silica from sandstone and carries this silica-rich solution into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually, opal is formed. Though the water evaporates, the opal gemstone still contains 13% water.
Opal: Color
Opal can come in many different colors. In its fundamental form, the opal is colorless, but this is rarely found. The difference in color comes from the formation process of the water forming tiny spheres, all of which are usually uniform in size and order diffracting light within the stone thus creating various colors of the rainbow. The more uniform the size of the spheres, the more intense, brilliant, and defined the color will be. If the spheres are random in shape and arrangement, common or colorless opal is formed.
The color of the opal depends solely on the uniformity of the tiny spheres. In smaller spheres, the spectrum of blues and violets would show. In larger spheres, the colors of orange and red will show more on stone. These stones are highly valued since they show more "play of color" or spectral colors when rotated.
Opal: Different types
The opal can be found in many varieties and types. Fine quality opal surprisingly, is rarer to find than that of rare rubies and emeralds. Below are different types of Opal that can be found:
Black Opal - These types of opals are the rarest and most valuable of all opals. These opals usually come in bar form. Despite the name, these types of opals have the complete colors of the rainbow but the body is of dark colors of black, brown, blue, or gray.
Boulder Opal - These types of opals are usually found in the mining fields of Queensland, Australia. This type of opal is often cut with the ironstone left on the back, as the opal seam is usually quite thin. They can be found in many different forms and colors: its surface can be smooth or uneven, with the opal occurring as a solid piece on top of the ironstone or showing as flashing flecks of color throughout the ironstone.
Common Opal - These types of Opal does not display any "play of color" and are classified as non-gem quality Opal. These types of opals are inexpensive and hold very little value.
Synthetic Opal
Synthetic opals are created in laboratories and are hard to tell apart from natural ones without the use of laboratory. The first synthetic opals were created by Pierre Gilson in 1974. He used a synthesizing method which is called the flocculation method. This method involves producing colloidal silica and separating and eliminating spheres using the sedimentation process. This process takes the course of some months to produce.
There are also man-made stones such as doublets and triplets. Doublet Opal is made of thin slices that are glued onto silica material, glass, or ironstone. The dark blackening gives the opal a more enhanced color. Triplet opal is made from three pieces, which consist firstly of a flat thin slice of precious opal, secondly a layer of common opal, glass, or porcelain that has been darkened, and thirdly a layer of quartz. Triplet opals are usually cheaper than doublet opals due to the fact that doublet carries a higher content of precious opal.
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