Table of Contents
Minerals are substances found in nature and they are solid with a crystal structure and are formed by geological processes. A gemstone or semi-precious stone is a piece of mineral crystal that has been cut and polished to make jewelry and other accessories. Stones and crystals are not just a fashion accessory. As a matter of fact, they have been used for millennia for awareness and even healing purposes. Since time immemorial, crystals and precious stones have been used to make sacred things and talismans, etc. Raw Opal is one such precious stone.
The interesting thing about the opal is that it is a hydrated amorphous form of silica and is classified as a mineraloid and not a mineral. A mineraloid has chemical compositions that vary and opal has a non-crystalline nature. This stone is known for its flashing colors known as play-of-color. Opal has a composition similar to that of quartz. However, what makes it different from quartz is its water content. The water content of the stone usually varies between 3 and 9%, but it can reach up to 20% depending on the variety.
Raw Opal origins and its mining
The first opal discovery was made in Australia and dates back to 1849. The stone was discovered by the German geologist Johannes Menge. Production began at White Cliffs (New South Wales) in 1890 and at Opalton (Queensland) in 1896.
The interesting thing with raw opal is that it is one of the few stones that can be affordably extracted by individual miners. The simplest form of mining is by shaft-sinking, done with a spade and a pick. A shaft is sunk until opal dirt is found. Some explosives will also be required and a hand-pick is then used to extract any opal found. Long ago, most mining for raw opal was done as a 2-man operation.
Of course, sinking a hole in areas known for the opals is not guaranteed to offer anything except perhaps opalized seashells or fossils from long ago. There has been an increase in the use of mining machines since the 1970s, and tunneling machines have also been introduced to streamline opal mining and to also increase productivity.
Australia – the premier opal discovery place
Australia is probably the most renowned area as being a source of precious opal and you can say that the land down under, because of several discoveries of raw opal in the early 1900s put the country ahead when it comes to opal production.
Famous mining areas for raw opal in Australia include, among others, Lightning Ridge, Coober Pedy, Andamooka, and Mintabie. It was in the 1800s that the production of raw opal started in Mexico and the country is particularly well known for its fire opal. Other areas where discoveries of opal were made, is Ethiopia, Brazil, Peru, Guatemala, Hungary, and others Opals has also been produced in the United States.
In fact, the town of Coober Pedy in South Australia is a major source of opal, and in fact, the world’s biggest and most valuable opal known as ‘Olympic Australis’ was found in 1956, weighing 17,000 carats. The raw opal was 11 inches long.
Another famous opal is the Fire Queen which comes from Lightning Ridge. This particular opal has been described as a ball of fire and referred to as ‘beautiful beyond description’. J.D. Rockefeller added beauty to his collection in 1949 for the sum of £75,000.
The Mintabie Opal Field, fairly close to Coober Pedy, has also produced a lot of crystal opal and that includes the black opal. Another major producer of matrix opal and black opal is Andamooka as well as Lightning Ridge.
The first discovery of common raw opals in Australia was made near Angaston by German geologist Johannes Menge in 1849. Production of precious opal began in NSW in 1890 and at Lightning Ridge in 1905.
At first raw opal was sent from NSW to Germany to be cut and polished. However, professional cutters started emerging, and the first recorded cutter was Charles Deane.
When Australian opals appeared on the world market in the 1890s, jealous Hungarian mines spread rumors that they were not genuine. By the year 1932, the Eastern European mines were not able to compete with Australia’s high-quality stones and they stopped production so that Australia is the premier raw opal producer.
There has been exploration for opal in the Hebel-Dirranbandi area of Australia, near the Queensland/New South Wales border where the Lightning Ridge opal field is found. You will find shaft and open-cut mining taking place for raw opal.
Australia has their black opals from Lightning Ridge, white opals from South Australia, and the Queensland boulder. So essentially, opal is a result of unique weather conditions – rains that drench the ground rich in silica. The rainwater trickles down into the earth, carrying silica-rich solution
Raw Opal – A Popular choice for Jewelry
People have mined opals for thousands of years and the gem is popularly worn in jewelry. Many people like to wear the jewelry as a pendant, near their heart as it is said to release pent up emotions and give one a sense of freedom.
The raw opal is not difficult to cut and interested people can actually learn to do it, They just need to use the right opal cutting equipment. Anyone who learns to cut opal will need to find the best way that the color can be exposed, taking into account imperfections.
The display of colors
Opal is a beautiful gemstone, displaying lots of colors. With faceted gemstones, the person doing the cutting lays in a pattern of facets at calibrated angles and transforms the raw opal into a brilliant gem. It is the size of the spheres inside the structure of an opal that will predict what colors are visible to us.
The light passing through the opal is first deflected, and then it is diffracted, and finally, colors are emitted from the light rays in the stone. Opals appear iridescent and multi-colored because when moving the stone, light hits different spheres at different angles, radiating all the colors.
Expert craftsmanship a must
With opal, you can say that beauty of the stone is often hid in the stone and it is the skill of the cutter that determines whether the beauty will be enhanced or diminished. Fortunately, with faceted gems, mistakes can be corrected but with the opal, a wrong cut can result in the stone’s beauty being lost for good.
When opals are cut for jewelry, they are commonly turned into what is known as oval cabochons. The reason for this is that this particular shape gives off the best color display and also prevents the stone from breakage.
Today, opals can be found in every kind of jewelry, from rings to bracelets to earrings and necklaces. Because of the low density, opals that are big are still included in pieces of jewelry. Because of its low level of hardness, it can be scratched more easily than other gemstones.
It can be immensely satisfying to work on revealing the hidden beauty of the raw opal. If you do research, you will find online tutorials on how to change the raw stone and turn it into a precious gemstone. If you opt to take your opals to a jewelry maker, you will have to dry them slowly.
Curing the Opals
You need to remember that opals have quite a bit of water content, and if they dry too quickly they can crack. It is for this reason that many people keep opals in water until they are sold. Opals are, however, cured to avoid extreme dryness and cracking which can damage the stone.
When you do store finished opals, it is best to keep them away from sources of heat or cold. Other people say it is not necessary to store them in water or oil but that they should just not be subjected to sudden changes in temperature.
Features of Raw Opal
Opal is a transparent stone, not milky. It is soft, rating 5.5 to 6.5 on the hardness scale. Some opals crack when they dry too quickly after being mined. They can be somewhat porous if they are allowed to dry too quickly. The stone has a long history and there are many myths about the stone, making it more interesting and mysterious.
There are many varieties of opal – common Opal, crystal opal, water opal, white opal, moss opal, pink opal, precious opal, fire opal, and many others. Essentially though, there are 2 broad categories of opal, and that is precious opal and common opal. it is the common opal that does not have that play-of-color., and common opal, which does not.
They also come in lots of colors, from white to orange, green, violet, blue, shades of red, white, and colorless. The stone is known for its fire or play of colors because of diffraction. This phenomenon of flashing colors is because of diffraction and is not related to the color of the opal. The colors seen in the opal’s fire depends on the size of the spheres as well as the angle of viewing.
Opal is October’s birthstone and this is also the stone given for when you have achieved 14 years of marriage to the same person.
The weather’s role in forming opals
The many variations in the types of raw opal you get will depend on a few factors, and the weather, with its wet and dry periods, creates silica. In fact, special conditions must prevail to provide a unique situation for the production of a variety of opal. Some experts on the opal say that there need to be acidic conditions to form silica spheres.
When evaluating the opal, certain features are taken into account –
- The opal’s color – particularly the colors displayed in the play-of-color, with red, orange, and green being the dominant hues. Bright colors are preferred to faint colors.
- The pattern – play of color occurs in 3 patterns, but regardless of the pattern, the colors must be bright.
- Clarity of the opal – this is its degree of transparency, and what- and if there are inclusions. Because opal is formed from rain falling, it contains moisture, but if the opal loses some of that moisture, it can develop a series of tiny fractures that are known as crazing, and this is a pity as it detracts from the beauty of the opal.
As a matter of interest, the raw opal Boulder, found in Queensland, forms in a way somewhat different to other kinds of opal. It forms inside an ironstone concretion, formed because of ionization.
The raw opal forms in ironstone boulders, from a few centimeters to up to 3 m across. The opal occurs as a filling between the concentric layers in the ironstone. Unlike other sedimentary precious opals, boulder opal is attached to the ironstone.
Some of the biggest opals in the world
The largest gem-quality opal in the world weighs 4.72 kg
The Jupiter Five – 5 kg, the largest piece of unworked opal.
The Opal of Halley’s comet is the largest black opal in the world.
Galaxy Opal was listed as the world’s largest polished opal in the year 1992
Cutting and polishing raw opal is a specialized skill, and usually, the rough opal is bought from opal miners as parcels. Opal cutting can produce unpredictable outcomes, but once the cutter has decided which pieces are worth cutting, the piece of opal is cut into a basic stone shape.
The most basic idea which any opal cutter needs to keep in mind is to keep the stone as large as possible, Water is used to cut opal to avoid overheating. Once cut, the face of the stone is decided on, considering which side has the best color for the stone. cabochons