Modern & Carbochon Birthstone – Opal
Traditional Birthstone - Tourmaline
Zodiac Stones for October
Libra Sept. 23 – Oct. 23 Chrysolite (Peridot)
Scorpio Oct. 24 – Nov. 21 Aquamarine
OPAL – pronounced (ō‘pəl) .
A natural hydrated form of silica. Opal is a relatively common mineral in its common form, which is known as common opal and lacks the play of color for which gem, or precious, opal is known. All opal is of relatively simple chemical composition, SiO2 · nH2O. The hardness of opal on the Mohs hardness scale ranges from 5 to 6.
The color of common opal ranges from transparent, glassy, and colorless to white and bluish white. The luster of the stone can go from vitreous to pearly. Precious opal has a play of color that is the result of white light being diffracted by the relatively regular internal array of silica spheres. Semiprecious Opal is beautiful but it does not have the fire and brilliance of a precious opal. Because opal is a hydrous mineral, certain opals from specific geologic occurrences may crack because of water loss. Therefore, considerable care is required in the polishing and handling of opal.
Several trade terms are used to describe the appearance of precious opal based on transparency, body color, and the type of play of color. Some of these terms are black opal, which is translucent to almost opaque, with dark gray to black body color, with play of color; fire opal, which is transparent to semitransparent, with yellow, orange, red, or brown body color and with or without play of color; harlequin or mosaic opal, in which the play of color occurs in distinct, broad, angular patches; and matrix opal, which consists of thin seams of high-quality gem opal in a matrix.
The name opal probably is derived from the ancient names for the stone. Sanskrit; upala which translates “precious stone”, the Greek; opallios which translates “color change”, and the Latin; opalus which translates “stone from several elements”. It has been mined for centuries, at least since Roman times when they extracted the opal from areas now within the Czech Republic. The Aztecs made use of local Mexican sources as did the Spaniards when they exported the material back to Europe.
Australia produces around 97% of the world’s opal. 90% is called ‘light opal’ or white and crystal opal. White makes up 60% and all the opal fields produce white opal; Crystal opal or pure hydrated silica makes up 30%; 8% is black and only 2% is boulder opal.
The town of Coober Pedy in South Australia is a major source of opal. Common, water, jelly, and fire opal are found mostly in Mexico and Mesoamerica. Another Australian town, Lightning Ridge in New South Wales, is the main source of black opal, opal containing a predominantly dark background (dark-gray to blue-black displaying the play of color).
Boulder opal is found sporadically in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south.
A source of white base opal in the United States is Spencer, Idaho. A high percentage of the opal found there occurs in thin layers. As a result, most of the production goes into the making of doublets and triplets.
The state gem stone for Nevada is precious black opal, which is named for the true black opal found in Virgin Valley, Humboldt County, Nevada.
OTHER TYPES OF OPAL
Fire opal is a translucent to semi-opaque stone that is generally yellow to bright orange and sometimes nearly red and displays pleochroism at certain angles.
Peruvian opal is a semi-opaque to opaque stone found in Peru which is often cut to include the matrix in the more opaque stones. It comes in various shades of blue and pink. It does not display pleochroism.
African Opal is a semi-opaqie to opaque stone found in Africa. It is found in various shades of white, yellow and brown.
The Traditional birthstone for the month of October is Tourmaline.
The two Zodiac signs that fall into October are Libra and Scorpio. For Libra the birthstone is Peridot or Chrysolite and for Scorpio it is Aquamarine.
For ages people have believed in the healing power of Opal. It is reported to be able to solve depressions and to help its wearer find the true and real love.
Opals are supposed to further enhance the positive characteristics for people born under the zodiac sign of Cancer. Black Opal is recommended to those born under Scorpio, and Boulder Opal is the lucky stone for Aries.
Tourmaline – pronounced: tour·ma·line (tʊr’mə-lĭn, -lēn’)
Tourmaline seems to have a special place in the hearts of mineral collectors as well as in that of gem and gemstone enthusiasts. Its nearly universal popularity is based on two very important facts: first, it is a bright and beautiful gemstone that can be found in just about any color; and second, materials that are of acceptable quality are affordable to most purchasers.
The word “rainbow” is used figuratively to describe tourmaline. In reality, it is a well recognized fact that tourmaline’s diversity in color is not limited to the seven colors of the rainbow. Tourmaline can be colorless to just about any color, hue, or tone known to man. And if range of colors among different tourmalines is not enough, individual crystals can vary in color along their length or in cross-section.
The variations in color along a crystal’s length give rise to the bicolor and tricolor tourmalines which have multitudes of color combinations. The variation in color in cross-section can be concentric, as in the case of “watermelon” tourmaline, a pink core surrounded by a green rind. Or the variation may have a distinct triangular pattern as in the case of liddicoatite
The United States is a large producer of Tourmaline as is Brazil.
California has ranked as high as second and as low as sixth in the value of natural gemstone produced in the United States. The State’s fabulous tourmalines were discovered by the gemstone industry in the late 1870′s or early 1880′s. The caveat, discovery by the gemstone industry, is used because Native Americans discovered and used these beautiful tourmalines long before that.
Since their discovery, the tourmaline deposits in Riverside and San Diego Counties have had more tourmaline produced and of greater value than any other deposits in the Northern Hemisphere. In fact, it is probable that only the deposits in Brazil have been more productive.
One of the reasons for the productivity of the area is the longevity of the individual mines. Many of them have operated intermittently from the 1890′s until the present. The famous Himalaya Mine is quite likely the best example.
Records indicate that from 1898 until 1914, the Himalaya was the world’s largest producer of tourmaline. Furthermore, the records indicate that in 1904 production from the mine was at least 5.5 metric tons. In 1989, 84 years later, a single pocket in the mine produced more than 0.5 metric ton of tourmaline.
The mine operated continuously from 1898 until 1914, after which it operated sporadically until 1952. At this time, it once again began continuous operations that lasted until 1964 when it returned to intermittent operation until 1977. Since then the mine has been in operation under the direction of Pala International.
California tourmalines come in all colors except certain shades of blue and yellow. They also occur in bicolor, tricolors, and concentrically and laterally zoned combinations. Because of the large size of the crystals available, some large stones have been cut from California tourmaline. A 400-carat pink-red stone has been cut, as well as a flawless 75 carat green to pink bicolor and flawless 30- to 40 carat green to colorless to pink tricolor stones.
California deposits should continue to produce quantities of faceting, carving, and cabochon grade, as well as specimen-grade tourmalines for some time into the future. In late 1992, a new deposit of tourmaline was discovered in Riverside County that could result in greater production over even a longer period of time.
Maine – Tourmaline was the first gemstone mined in the United States by miners other than prehistoric man or Native Americans. Tourmaline mining began at Mount Mica, ME, in 1822 and, with starts and stops, has continued to the present. In 1992, operations at Mount Mica produced both gem-quality and mineral specimen tourmaline.
Over the years, mining operations on Mount Mica produced hundreds of kilograms of tourmaline. Museums and private collections around the world contain outstanding examples of tourmaline from the deposit. The largest reported crystal from the site apparently is one that is 39.4 centimeters long, 17.8 centimeters wide, and weighs about 14.3 kilograms. Apparently, a flawless, blue-green 256-carat stone is the largest cut stone from Mount Mica.
Mount Mica may have been the first tourmaline producer in Maine, but it is by no means the largest. Newry Hill, a spur off Plumbago Mountain, or more specifically the Dunton Mine on Newry Hill, is the most prolific tourmaline producer in Maine. Since its discovery in 1898, production from the mine has exceeded thousands of kilograms of high-quality tourmaline. The mines ability to yield large quantities of quality tourmaline was clearly demonstrated by Plumbago Mining Corp. The company reported that from October 1972 until the Fall of 1974, it produced more than one metric ton of fine-quality tourmaline.
Maine tourmalines come in a wide variation of colors, deep grass green to light green to yellow-green to blue green. They are also found in all shades of red, from pink to deep red, and blue-green to light blue to deep blue, and as colorless crystals. The State’s mines also produce bicolor and watermelon crystals. The colors can be very fine and some believe that Maine tourmalines set the standard for non-chrome green tourmaline.
Another misnomer is “Smokey Topaz” this is actually Smokey Quartz. By naming is Smokey Topaz, jewelers felt people would pay more. Smokey Quartz is a very popular stone and the better cuts are moderate in price.
