What is an Opal ?
Opals as a species are very unique and have their own descriptive words. Opal is also the most delicate gemstone that is usually worn and requires special care.
Opal is one of the most popular gemstones and the birthstone of October. A precious and beautiful opal can flash any color of the spectrum with intensity and color quality. The best opals compete with the price of expensive diamonds, rubies, sapphires and emeralds.
Different types of opal are found in stocks around the world. Three popular types that may surprise you: Fire Opal is known for its bright colors of red, orange and yellow - the colors of fire! Boulder Opal Opal is attached to the host stone. It can be amazingly beautiful! Ordinary opal has a color, pattern and beauty that can be anything but ordinary. In terms of chemical formula, opal is a hydrated silicon dioxide with the chemical composition SiO2.nH2O. It is amorphous, with no crystal structure and no known chemical composition (contains a variable amount of water, as indicated by "n" in its chemical composition). Opal is therefore a mineral instead of a "mineraloid".
In literary writings opal is compared to volcanoes, galaxies and fireworks. Admirers gave extraordinary names to great opals such as Pandora and the light of the world. In ancient Rome, this gem was a symbol of love and hope. The Romans named it - opalus - which was synonymous with "precious stone".
In 75 AD, the Roman scientist Pliny was surprised to find that this kaleidoscopic gem contained ruby red, emerald green, topaz yellow, sapphire blue and amethyst purple.
Many cultures have attributed transcendental roots and powers to opal. Arabic legends say that these were created by lightning from the heavens. The ancient Greeks believed that opal prophesied to its owners and protected them from disease. It has long been considered a symbol of hope, purity and truth in European culture.
Opal is a stone born in October. Some people think that someone born in another month is unlucky to wear opal. But these particular superstitions stem from a novel written in the 1800s (by Anne Geierstein by Sir Walter Scott) and there is no ancient belief or experience behind this thinking. In fact, for most of history, opal has been known as the luckiest and most magical gemstone because it can show all colors. It was once thought to have the power to sustain life.
The term "common opal" refers to opals with a matte or waxy appearance. These stones are rarely cut and have a wide range of colors. Common opals are often fluorescent. The terms "precious opal" as well as "noble opal" refer to opals of any color that display fire or play of colors.
· Black Opals
These opals have a black body color with fire, which is often spectacular on a dark background. Body color can also be bluish, dark or brown. Please note that the term "black opal" may also refer to a black potch covered with a thin layer of crystal opal, which is displayed in black and white later.
· White Opals
White body color with fire.
· Prase Opals
These green to yellowish-green opals, clear to opaque, are very similar to chrysoprase. Chrysopal is a type of golden green.
A brownish-gray opals with a flexible structure is called Menilite.
An opaline (opal-like) silica found in the joints of some bamboos is called Tabasheer.
· Girasol Opals
This opaque is semi-transparent to semi-transparent and has a moving and vibrant light effect, Girasol Opals are like moonstones.
· Contraluz Opals
Rare Contraluz opals are commonly found in Mexico but are also found in Australia. These transparent opals show color play in both transmitted light and reflected light.
Hyalites or jelly opals with a clear, colorless or white to gray sheen with a clear glassy sheen. Pale and without any color, they are rarely faceted and generally have no stone significance.
· Moss Opals
Moss opals are white to brown and opaque and contain dendritic components that are similar to Moss.
· Hydrophane Opals
Rop Hydrophane Opals become clear with a light and matte color and show play color when soaked in water or oil. They are sometimes referred to as "magic stones".
Siliceous sinter or geyserite is a glassy opal that forms around hot springs and geysers. These huge structures do not have a face for jewelry.
· Diatomaceous Earth
Tripoli or diatomaceous earth is composed of fine and powdery opal masses and siliceous remains of a microscopic marine animal called diatomaceous earth. This material is mostly used in polishing materials and fillers.
· Cacholong Opals
Cacholong Opals, which are often bluish white, clear to dull and very porous, look like porcelain. This stone, also known as kalmuck agate opal, actually sticks to your tongue.
· Jasper Opals
These reddish-brown opaque opals look like jaspers.
· Chrysocolla Opals
The blue color of these opals is due to the presence of finely dispersed components of chrysocolla, the mineral copper phyllosilicate.
· Liver Opals
Commonly referred to as brown opals.
· Resin Opals
These opals are common yellowish brown opals with a waxy to resin luster.
· Iron Opals
Common red to yellow opals are called Iron Opals.
· Louisiana Opals
These gems are composed of quartz, opal and pyrite and are extracted from the state of Louisiana.
· Oolitic Opals
These opals have small black or brown spherical components similar to fish roe and play with many colors.
· Wax Opals
Waxy opals with waxy luster are called Wax Opals.
· Star Opals
the asterism or star effect is extremely rare, caused by a defect in the arrangement of their silicate spheres. Therefore, the stellar effect of these stones is different from other gemstones, such as sapphire, due to the components.
· Natural Opalite
The term "opal" is commonly used to refer to a plastic or glass opal simulator. However, there are types of natural opals that are sometimes known as opal. This common variety of opal is available in green, lavender or purple and can even show cat's eye.
· Opalized Wood
Opalized Wood is a type of fossilized wood that is made of opal instead of chalcedony or other minerals. It is almost always composed of common opal, colorless, but rare cases of fossilized wood composed of precious opal are known. It is commonly thought that stoneware made of opal is made of chalcedony because many people do not know that stoneware can be opaline.
· Fluorescent Opal
Most opals glow dimly or fluoresce under an ultraviolet lamp. However, some samples show a significant fluorescence. This typical example of rough moss opal from Virgin Valley, Nevada, glows a bright green under UV light. The photo on the left is taken under normal light and the photo on the right is taken under a shortwave UV lamp.
· Water Opals
The body is clear or colorless and may have a fire.
· Crystal Opals
These opals are rich in colorless, translucent to translucent light, in colors reflected by light. Black crystal opals are from clear to semi-transparent with a dark body color and play color.
· Milk Opals
These clear, translucent white stones may also be yellow or greenish in color.
· Fire Opals
These stones are clear to transparent with a yellow, orange or red body color, may or may not show color play. "Fire" in their name refers to the color of their body, not to the play of color. These stones are also called Mexican opal or sun.
· Boulder Opals
Thin opal seams formed in iron ore. These gemstones come in a variety of colors and represent a dazzling fire supported by a brown iron ore matrix.
Artificial opals may have strong color representations, usually in the form of mosaics. With high magnification and backlight or high, you can find a cellular structure, snake-like skin or chicken wire in the pattern. Under high magnification with transmitted light, the synthesis may show a dendritic structure.
Synthetic opals do not phosphorize. They may also stick to the tongue. Artificial white opal can show columnar structures from the side.
Opal is a soft plastic imitation or simulation and can be explored with a sharp needle. They are not phosphorus.
Glass simulators usually contain glass bubbles and signs of rotation, and they also do not phosphorize. Their specific gravity (SG) and refractive index (RI) are usually higher than natural opal.
· Notes on Hydrophanes
Hydrophane opals usually absorb water and chemicals and can generally negatively affect their appearance. Keep them dry and away from any contamination.
· Impregnation with Black Plastic
Opals the appearance of opal black. Stability is excellent. It is somewhat common. It is recognizable because the cut parts have very low SG values and dye concentrations in the cracks. Sometimes major laboratory equipment is needed.
· Impregnation with Oil, Wax, or Plastic
Improves color play in opal. It has poor stability for oil and wax. It can be detected by testing the hot spot. Plastics require major laboratory equipment.
· Impregnation with Smoke
This method darkens the color of the body. It can be detected by magnification and low SG (it may float in water until it is sufficiently absorbed and drowned). It loses color when wet but returns when dry.
· Treatment with Aniline Dye, Silver Nitrate, or Sugar
This method also darkens the body color. It has good stability. Shows magnification of black concentrations.
Australia is one of the best known regions for opal production in the world. Unfortunately, the deposits have been so badly worked out that they are disappearing. Opal miners now work less in the opal field than they did 10 years ago, and new discoveries are very rare. These factors, in addition to global demand, put a lot of pressure on opal prices.
The first Australian opal discoveries probably took place around 1850, but modern Queensland trade made major discoveries around 1872.
Opal is mined from Piaui Slate, northern Brazil, as well as near Manaus, northern Brazil. It is a fiery white gem and sometimes resembles high quality Australian white opal. Brazilian opal may not be ranked as the most durable, waterproof and heat sensitive opal. Dr. Joel Arem reports that he kept a cut gem on a candle flame for 30 seconds without any side effects, and it appears to be abundant and is often shipped to Hong Kong as Australian opal It is cut and sold there.
· Czech Republic and Slovak Republic
In ancient Roman times, a spring near the village of Czerwenitza (formerly Hungary) was known to produce opal as a seam in the grayish-brown andesitic rock. This opal has a mosaic display of strong colors and looks very attractive against the milky white background color. Most of these are opals with a Harlequin pattern.
Ethiopia has been a source of opal since ancient times, with the recent discovery of precious opals in 1994 and 2008. The opal near the town of Wegel Tena shows a spectacular play of color.
Mines known before 1843, perhaps much older, as vessels in reddish-black tractite. White opal contrasts with the dark color matrix. The not-so-large pieces are rarely very spectacular.
Very few minerals are known in nature as thin seams in dark rock. Most of it is water opal and is similar to Mexican minerals. White opal is similar to low-grade Australian opal. Indonesia produces a very unusual black agate consisting of reddish flecks of color swimming on a light but very dark brown body. Most gemstones from this place are very small and production is very low.
Mexican opals form in siliceous volcanic lava, in cavities, and in many areas. Yellow and red fire agate is obtained from a trachyte porphyry in Zimapan in Hidalgo. Hyalite and precious opals are made completely clear, colorless and rich in fire in San Luis Potosi. Queretaro is also a popular area for opal production. Good Mexican opal in large sizes (over 50 carats) is very rare but one of the most beautiful.
There is green prase opal,that is colored by nickel.
Nickeliferous opal is similar to chrysoprase in Tanzania with brown limonite. Its RI and gravity are lower than those of chrysoprase. The size of the stones is also small.
· United States
In the United States, opal was first discovered around 1900 in Virgin Valley, Humboldt, Nevada, commonly seen as cracks and seams in opal wood. Magnificent but very juicy, this opal has a high tendency to crack due to water loss when exposed to air. The complete skeleton of extinct animals has been replaced with precious and delicate opal. A similar opal is produced in Idaho.
Several large, high-quality opals have received individual names, such as diamonds. Some of the most popular ones include the following:
· Olympic Australis: Coober Pedy; uncut was 127 oz.
· Noolinga Nera: Andamooka; 86 oz rough, 205-ct oval cut.
· Roebling Opal: Nevada (Rainbow Ridge); 2,610 cts (in the Smithsonian Institution).
· Light of the World: Lightning Ridge, Australia; 252, partly cut.
· Red Admiral or Butterfly: Lightning Ridge, Australia; 40-50 cts rough. Many regard this as the world’s most beautiful opal.
· Pride of Australia: Lightning Ridge, Australia; 226, partly cut.
· Pandora: Lightning Ridge, Australia; 711, cut.
· Smithsonian Institution (Washington, DC): Australian gems; 345, 155, 83 (all white); black opals of 58.8, 54.3, 44. Also 355 (black, Nevada); 143.2 (orange, precious, Mexico); 55.9 (colorless, precious, Mexico); 39 (pale yellow-orange, precious, Brazil).
Play of Colors in Opal
It has long been thought that the characteristic fire of opal, or the play of colors, is the result of iridescence. But with the advent of scanning electron microscopes in the world of science, we now know that this is the result of diffraction. This flashing or moving color phenomenon is not related to opal body color due to diffraction.
Different colors are seen in the fire of an opal and depend on the size of the spheres and the angle of view. For example, black opal derives its color from volcanic ash, but inclusions have nothing to do with the play of color, and this is due to small spheres of silicate. For blue and purple colors should be less than 1500 angstroms (Å), but for the production of orange and red opal should not be larger than 3500. In other words, 20,000 constituencies is about the size of the last sentence. (Angstrom is one tenth of a billionth of a meter).
Opal is a very common mineral found all over the world. Most opal is "common opal" or opal, which lacks the colorful flashes known as the "game of color". Some people usually use the name "potch" for this type of opal.
Most ordinary opals are not noticeable in appearance and are almost completely ignored in this regard. It is sometimes thought to be quartz or chalcedony - but there is a surprising amount of common opal.
Rare examples of play-of-color opal are known as "precious opals". If the play-of-color is of high quality and sufficient, this material can be used to produce precious stones.
If you look at a sample of precious opal in bright light, the play of color is seen in three modes: 1) when the stone moves, 2) when the light source moves, or 3) when the viewing angle has changed. .
The word "opalescence" is often misused. Some people mistakenly believe that "opalescence" and "play of color" are the same. A common definition for opal stone play of color is "common opal pearl polish". Most opals, on the other hand, do not have a pearly sheen, even if polished.
How does "play of color" happen ?
An opal is made up of millions of microscopic silica spheres arranged in a regular grid. These spheres are very small, about 1/2 micron, and act as a diffraction grating. As light passes through, it scatter into the colors of the spectrum. The size of the spheres and their geometric packaging determine the color and quality of the diffraction light.
Opal may be treated by saturation with oil, wax or plastic. Two or three opals are thin slices of opal attached to a base material and covered with a thin dome of clear quartz. The safest way to clean opal is with hot water and soap. Other cleaning methods may damage the opal or filler material. Note that prolonged exposure to water may reduce the adhesive in opal twins and triplets. Even natural opal may break if exposed to high temperatures or sudden temperature changes.
Opal hardness ranges from 5 to 6.5 in Mohs. Store the opal alone to prevent scratching, which is done with harder jewelry. Diamonds, rubies, sapphires and emeralds are just some of the gemstones that can scratch opal.
Opal as gift
People born in October enjoy opal to celebrate their birthday. October birthday stone has endless color combination and beautiful coloring features. Agate is also a stone that has been given to celebrate the fourteenth wedding anniversary.
The October birthstone’s dramatic play-of-color has led writers to compare it to fireworks, galaxies, and volcanoes. In Arabic culture, it was believed that opal had lightning and fell from the sky during a thunderstorm. The ancient Greeks thought that opal was a gift for divination and protection against disease. Europeans have long regarded opal as a symbol of purity, hope and truth. For hundreds of years it has been believed that giving opal is like embodying the virtues and powers of all colored stones.
Alexandrite is known as "Emerald by day, ruby by night" because it has one of the most dramatic color changes among gemstones, such as green in sunlight and red in incandescent light. The very precious habit of alexandrite color change is caused by the presence of minor impurities in the element chromium. The most desirable Alexandrite colors are those that have a very clear color change.
Citrine is a clear quartz, pale yellow and brownish orange, which is rare in nature. In the past, the color of its sobriety was confused with topaz. Citrine is the best-selling yellow to orange gemstone due to its attractive color, plus durability and affordability. Citrine can be an attractive option not only for topaz, but also for sapphire.