Business & Industry

Jun 1, 2015

All the colours at once

Opals are amongst the most beautiful stones in the world, and are one of the few types of precious gemstones. While diamonds, rubies, sapphires, emeralds and pearls have their own color, nonetheless wonderful, with opals you have all the colors in just one stone.

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It seems like magic the way an opal glows and refracts the light. That's probably why, unlike other opals mined in other parts of the world, the Australian opal is said to be the finest of them all.

Opals exist plenty in Australia: almost the totality, more exactly around 95% of the opals produced in the world come from here. Although there are several mining sites along the 'Great Inland Sea', or 'Great Artesian Basin', four of them have grown to be renowed for their production of opals, mainly for jewelry: Coober Pedy, Andamooka, White Cliffs and Lightning Ridge, each producing more of one or other kind, since the types of opals found vary from place to place, the White, or 'Milky' opal being found in South Australia, Boulder opal  in Queensland, and Black opal  in Lightning Ridge, New South Whales.

But first things first, let's talk about how opals come to be. Opals are an amorphous mineraloids, composed of silica and water, or in scientific terms, hydrated silicon dioxide, and it forms when it solidifies, after depositing as a gelatinous form. Opaline silica with a play of colour is a definition for the precious opal, and this term, play of color, was created specifically to describe this beautifully colored stone. This "play of color is a result of thousands of tiny spheres of silica, sized between 1500 and 3500 angstroms (1 angstrom is 1 ten millionth of 1 millimetre), that diffract the light. This interference makes it so that the colors shift and changes depending on the angle from which you look at it. Also, the size of these spheres will influence the color they refract: when they are bigger, we see orange light, when smaller, we see blue.

Now, the (more) interesting part. There are several types of opals, and two main varieties are considered: precious opal and common opal. The fist presents the referred play of color, while the other, much more common, does not, and it is mainly one colored, either white grey or black. Precious opal will have the play of color, it is a requirement to classify it as such. Opals of blue colour only are the most common, and red ones are the rarest colour.

The three main types of opals, mined by the biggest sites which we mentioned before, are denominated as white, black and boulder. This classification is determined by its tone, the degree of blackness. Black opals, the most valuable type, mainly found in Lightning Ridge, is characterized by a dark body tone that enhances the brightness of colour which is not as intense as in lighter opals. White opals come mainly from South Australia, and do not diplay the show of lights as brightly as the black opal. It is less valuable, nonetheless remaining beautiful and marvelous. The boulder opal is embedded into iron rock. It is formed when the silica settled in thin cracks, making the opal layer very thin. The main characteristic of this type is the fact that because it is so thin, the opal layer is cut with the ironstone left on he back. 

The value of the opal varies based on various factors that determine its quality: the tone, colours present, play of colour, pattern, brilliance, as well as the quality of the cut and polish, and the size of the stone. The price is attributed 'per carat', varying its value based on the previous characteristics: If a stone is better at each of them, its price per carat will be higher. But, the fact is, there is no better way of knowing than to take it out for an educated evaluation. It is not standardized, due to its numerous variations, unlike diamonds, that are easier to standardize.

So now that you know about these stones, doesn't it make you want to look at one, hold it in your hand, and observe the millions of years it took to look like that, the time it remained hidden away from daylight inside the earth made it so when it finally came out, it would be the most colorful and alive stone among the precious ones? Rubis may be red, saphires may be blue, but the color of the opal is every single hue.


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