PHYSICAL AND OPTICAL PROPERTIES OF OPAL
The term opal designates a family of minerals composed of silica and water with inclusions of various elements. Its chemical formula is SiO2, nH2O, it is hydrated silicon dioxide. The proportion of water varies from 1 to 27%. There is no crystal system. The density of opals ranges from 1.98 to 2.50, their hardness on the Mohs scale is 5.5 to 6.5. Under ultraviolet rays, opals have a white, yellow, greenish-yellow or green luminescence.
There are several varieties of opals. Noble opals, highly sought after in jewelry, exhibit a phenomenon of iridescence, that is to say they show a play of multicolored flashes of light. They are produced by the diffraction of light on silica nanospherules of homogeneous size and arrangement. Common opals, on the other hand, have heterogeneous or irregular nanospherules, and therefore have a single color.
Here are some types of opals:
- Fire opal, hyacinth red to fire red, transparent to translucent;
- Milky white opal, milky white to yellow-white or blue-white, translucent with a vitreous to matte luster; some contain veinlets and masses of manganese oxide, these are dendritic opals.
- Woody opal consists of opalized trunks or branches. The wood rings are clearly visible. This opal is fragile.
- The hydrophane (or opal matrix) is white, matte and sticks to the tongue. Rather opaque, it has the property of changing appearance if immersed in water. It then becomes more transparent and can become iridescent.
- Hyalite has a high transparency, it is colorless with slight blue or green nuances.
- Jelly opal is gray-blue with some play of light
- Harlequin opal has beautiful iridescent glitter in all colors, it is highly prized.
GENESIS OF OPAL AND ITS MAIN DEPOSITS
Opal forms when water leaches silica and deposits it on layers of sandy clay during a period of drought. It is sometimes found instead of shells or bones. The location of the gems in the mine is therefore unpredictable, they must be searched for by hand or with small machines to avoid the risk of breaking them.
In the past, opals came from Egypt, India or Saudi Arabia. Nowadays, it is Australia which produces 90% of the opals sold in the world, precious gems and of very high quality. These deposits were discovered by German geologist Johannes Menge in 1849. One of them, Lightning Ridge, revealed opalized dinosaur skeletons.
Other opal producing countries are Brazil, Guatemala, Honduras, Indonesia, Japan, Mexico, Russia and the United States.
ADVICE FROM OUR GEMMOLOGIST: HOW TO CHOOSE YOUR OPAL WELL?
There are so many kinds of opals, so many different colors that the first criterion of choice obviously remains the tastes of each one. However, the value of an opal depends on several criteria:
- the color of iridescence: the play of red light is the most sought after, followed by violet, pink and turquoise, which are very rare, and finally blue and green, which are more common.
- the intensity of the iridescence: in general an opal with a less prestigious color than others but with very bright and intense iridescences will have a higher price than a more sought-after color but with duller sparkles.
- transparency is also an important evaluation criterion, depending on the variety of opals.
- the pattern: for example, Yowah opals have mosaics of extraordinary colors, which make the stone look like stained glass or cloisonné enamels.
METALS COMMONLY ASSOCIATED WITH OPAL
The wide variety of opals gives free rein to the creativity of jewelers. We see this stone associated with gold, silver and the prestigious platinum.
OPAL STORIES AND LEGENDS
The word “opal” would come from the Sanskrit Upala, via the Greek “opallios” which would designate color changes.
Some Aboriginal groups in Australia have a very poetic legend in their mythology: the creator god once descended on Earth by sliding on a rainbow. No sooner had he set foot on the ground than all the stones would have started to sparkle, the same colors as the rainbow...
For Pliny the Elder, the opal was marvelous because it combined the colors and qualities of all the other precious stones.
It is said that Marc Antony dreamed of acquiring the magnificent blue opal from a senator called Nonius, with the aim of offering it to the beautiful Cleopatra. But the senator in question, rather than give up his stone, preferred to choose exile...
In India the opal is the symbol of the Trinity (Trimûrti) formed by the creator god Brahma, the preserver Vishnu and the destroyer Shiva.
It has long been considered a lucky charm and present in the treasures of European courts. This fine reputation was once shattered by the influence of a 19th century novel written by the Scotsman Walter Scott, in which a princess is accused of being demonic. She wears an opal on her forehead and, in contact with holy water, the gem loses all its colors and the princess is seized with pain… before disappearing, leaving behind only a handful of ashes.
VIRTUES AND BENEFITS OF OPAL
The Greeks considered the opal to bring hope and a symbol of purity. It had the reputation of increasing clairvoyance, making meditation and reflection easier, improving intuition.
Today in lithotherapy, we continue to attribute these virtues to opal. It calms and soothes, promotes love and tenderness, improves the sentimental life of Gemini and Aquarius. It opens the mind to spiritual life and restores vitality to tired people.
ASTROLOGICAL CORRESPONDENCES OF OPAL
Opal is the birthstone of people born in October. It is associated with several astrological signs: Aquarius, Gemini, Pisces, Cancer, Virgo... in Chinese astrology, it is the stone of the Serpent: it has mysterious depths, gives endurance and courage, and makes... invisible .
Opal weddings designate the 21st wedding anniversary.
The Science of Opal
Opal's internal structure makes it diffract light; depending on the conditions in which it formed it can take on many colors. Opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent. For gemstone use, its natural color is often enhanced by placing thin layers of opal on a darker underlying stone, like basalt.
Opal throughout History
In the Middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the color spectrum of the opal. It was also said to confer the power of invisibility if wrapped in a fresh bay leaf and held in the hand. Following the publication of Sir Walter Scott's Anne of Geierstein in 1829, however, opal acquired a less auspicious reputation. In Scott's novel, the Baroness of Arnheim wears an opal talisman with supernatural powers. When a drop of holy water falls on the talisman, the opal turns into a colorless stone and the Baroness dies soon thereafter. Due to the popularity of Scott's novel, people began to associate opals with bad luck and death.
Within a year of the publishing of Scott's novel in April 1829, the sale of opals in Europe dropped by 50%, and remained low for the next twenty years or so.
Opal's healing properties
Pink opal heals from cardiac disorders
Opal is really sensitive to shocks . You shoud not put perfume , soap or other cleaning products on it.