![]() See image, left – An electron-microscope photograph of of the ordered structure in precious opal, showing its light-diffracting spheres. It is these tiny spheres and gaps which hold the secret of the opal’s colour. The spheres in an opal are not only remarkably uniform in size but are packed, in gem quality opal, in a very regular array. In these gaps between the stacked spheres, a water and silica solution remains. These spheres of range in size from 1500 to 3500 angstroms (1 angstrom is 1 ten millionth of 1 millimetre).īecause they are spherical, there are tiny gaps remaining between the spheres (much the same as when marbles are placed together in a container). ![]() The spheres are formed because particles of silica spontaneously adhere to other particles which form around it. Over a long period of time, the solution settles and the water evaporates, allowing the gradual formation of layer upon layer of microscopic silica spheres. This solution fills voids or is trapped in layers under the earth, and opal begins to form. A silica solution forms when silica from under the earth mixes with water. To understand how this happens, it’s time for a lesson on the microscopic structure of opals īasically, opal is made up of water and silica (the main component in glass). Much like a prism, which can refract white light and produce a rainbow effect, opals diffract the white light which is coming from above, displaying those amazing opal colours. The answer, put simply, is the diffraction of light. The very idea that such magnificent colours have been hidden under the earth in darkness since ancient times, and pulled out of the ground to display their opalescence in the light of day, is truly staggering.īut what causes the colors in an opal? What is different about opal that makes the colours dance and play across the face and burn in every colour of the spectrum? The opal is arguably the most beautiful of all gems – at the very least it is highly unique and a true treasure of the earth. This captivating miracle of nature has been admired by people the world over for centuries, and highly sought after for use in jewelry, museums and collectors’ pieces. The pattern and arrangement of the colour which is displayed in an opal can take on many beautiful forms, and the movement of colour across the face of a stone is known as the ‘play of colour’. Unlike any other gem, opals can display all the colours of the rainbow in an iridescent, moving pattern of red, green, blue, yellow, purple, aqua, pink, and any other colour you can imagine. The colour of an opal is a magnificent thing. Most precious opal mined in ancient times came from what is now Slovakia.FAQ: What causes the colours in opal? How does opal get its colour? What is potch? Where do opals get their colours? What is the structure of opals? Why does opal have colour? In the Middle Ages it was said to bring good luck. In ancient times opal was considered to be a noble gem, and the Romans ranked it second only to the emerald. Simulants are man-made stones which are similar to opal but made from a different material.įire opal is mined in Mexico and Honduras, and several varieties of precious opal are found in India, New Zealand and the deserts of the western US. Scientists have been able to reproduce synthetic opal in a laboratory, and other "simulants" exist on the market. Various forms of common opal are mined for industrial use in abrasives, ceramics and insulation. Many chemicals can damage an opal due to its porous structure. ![]() Opals can be dehydrated when exposed to heat or chemicals. When warmed by the hand, water contained within an opal stone can change colors, making a stone particularly brilliant. This milkiness in many white and gray opals is due to an abundance of tiny gas-filled cavities. Precious opals are translucent to transparent and have a pearly opalescence revealing many flashing colors, which change as a stone is viewed from different angles. White opal, with lighter colors, and fire opal, with yellow, orange or red colors, are much more common. Black opal, with its very dark gray or blue-to-black color, is rare and highly prized. Pure opals are primarily colorless, but impurities usually impart various colors to them ranging from yellows and reds, due to iron oxides to black from manganese oxides and carbon. Opals are commonly found in volcanic rock, especially near geysers and hot springs, but can occur in almost any geological environment. When the silica solidifies it creates the gemstone opal which contains approximately 6 to 10 percent water. ![]() Opal is a form of noncrystalline quartz which is created from circulating, silica-bearing waters. The word opal comes from the Latin word "opalus," which means precious stone. ![]()
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