Why an Opal Doesn’t Hold Color Like a Green Leaf or Blue Car
February 1st, 2010 // 3:35 pm @ admin
A miner in Australia stands tired and alone next to a hole in the ground. He is surrounded by desolate plains of dirt. The sun is hot, there is no water, and the distance is distorted in all directions by waves of heat. With his back to the sun, he wipes hard dirt from an even harder stone until a shot of color pleasures his eyes. He sighs in relief and he would jump for joy if only he had the energy. On his journey home, bouncing down the dirt road, he places the opal on the dashboard to dazzle with light. He looks at it more than the road and he wonders how something so beautiful can be found in such an awful place.
He is not the only one who has wondered how a gemstone is made. Perhaps you’ve marveled how something so beautiful can be pulled from deep beneath the ground surrounded by common rock and dirt. There are thousands of different gemstones mined around the world. Everything from turquoise in Arizona, opals from Lightening Ridge to Diamonds from Zimbabwe is sought after and mined and sold and cut and sold again and again until some lucky person wears it in a piece of jewelry. But how are they made? There are many factors involved in the development of a gemstone: water, temperature, pressure, time and of course the main ingredient, which determines what type of gemstone you will have in the end. One particular gemstone that has raised interest in many parts of the scientific world is the opal.
Opals are very interesting to scientists because of their inherent ability to manipulate light.
When light hits an opal it is divided into the separate wavelengths that display the colors of the spectrum: Red, Orange, Yellow, Green, Blue, Indigo, and Violet. If you look at opal beneath a very powerful microscope, you will see a dull picture of tiny spheres stuck together in a very familiar pattern. They look like oranges stacked on top of each other in the supermarket. This pattern, it turns out plays a very important roll in the beauty that we observe in an opal. It is important to note that it is the pattern alone.
Opal doesn’t hold a color like a green leaf does or a blue car.
It has what is called structural color or color that is derived from light passing through a particular structure. There are other occurrences of structural color found in this world: the wings of certain butterflies, wings of hummingbirds, abalone shell, and pearls to name a few. These amazing phenomena are all due to one particular factor in their make-up—-their make-up.
There are three different ways this happens in nature.
- The first one is part of genetic code. At the time they are grown or created, there is something in the hummingbird’s design that demands his wings to be made to diffract light and similarly the butterfly.
- Secondly, the abalone is a shelled creature that lives in the ocean and makes its shell from calcium carbonate molecules found in ocean water. The abalone knows that his shell will be much stronger if it is stacked in a brick-like formation versus a random pattern of all different sizes particles. And it just so happens that this formation also diffracts light and is very beautiful.
- Finally, opal is created deep in the Earth from a liquid mixture of silica and water. The silica is extracted from the soil by rainwater and is filtered through rock and into hollow pockets where it collects and inevitably settles into a hard, precious gemstone. It is the luck of the miner that determines if it will ever see the light of day.
Now there is a new way to display this incredible phenomenon in a science project from NanoScienceKits.org. In a classroom setting, for the first time, kids and teachers can grow an opal mimicking the way it is grown in the Earth. Starting with the same silica solution and a test tube, over a period of weeks, they can watch the progress of these tiny spheres stacking gently and deliberately in the that special structure. This Chemistry experiment is simple and amazing. It will inspire children to come away with an understanding of the beauty that has awed royalty and driven markets and prompted miners to blaze the Australian heat day after day for decades.
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