October Birthstones
Opals
Opals, along with tourmaline, are known as the birthstone for the month of October. The majority of the world's supply of opals come from Australian mines.
Opals lack a crystal structure which is the accepted standard when defining a mineral. While some references still classify opal as a mineral, it is actually a mineraloid: an amorphous, inorganic substance lacking a crystal structure. The classification is Hydrous silicon dioxide with the water content ranging from 3% to 21% of the total weight, but is usually between 6% to 10%. It measures at 4.5 - 6.5 on the MOHS scale of hardness.
Opals can form in all mineral environments, especially igneous environments, but does not occur in crystals, except when it forms as a pseudomorph, where one mineral chemically replaces another mineral without changing the external form of the original mineral. It often pseudomorphs after organic matter such as wood, shell, and bone. (http://www.minerals.net/mineral/opal.aspx)
Opals are a huge group of gemstones that are separated into two basic types, precious opals and common opals. Precious opals are those that exhibit the wonderful display of color, iridescence, while common opals are more opaque and lack color play. Some reference this play of color as fire or flames however this is an incorrect description. Fire or "flames of color" are caused by light dispersion (http://www.bwsmigel.info/lesson6/de.optical.phenomena.html)
Iridescence: This phenomenon is seen as a multicolored, surface effect. It is caused by diffraction. As white light passes through very small openings such as pores or slits, or through thin layers of material which differ in refractive index, a prism effect causes it to separate into spectral colors. These may then be seen on the surface, or in some cases in the interior, of the material. Iridescence is responsible for the everyday observations of the spectacular colors seen in the metallically shimmering neck plumage of male Mallard ducks, peacocks and some hummingbirds, or as light catches the surface of a soap bubble.
When combined with interference, where the slightly out of phase color waves bouncing off different layers overlap as they reflect, a loss of some colors and a reinforcement of others can take place giving rise to dramatic color blocks, which may shift with viewing angle.
Iridescence is the most widespread of the optical phenomena, we see its effects in: the "orient" of pearls, the displays of fire agate, "rainbow calcite", certain obsidians, and iris agate. It also creates the rainbow display of fractures, the beautiful colors of Labradorite, and, probably most well-known, the "color play" of precious opal. (http://www.bwsmigel.info/lesson6/de.optical.phenomena.html)
Play of color: Iridescence in precious opal is correctly called "play of color" or "color play". The incorrect term "fire" is often misused instead--> recall from Lesson 4 that "fire" is an acceptable synonym for dispersion. But, at least in this course, it is not an acceptable synonym for "play of color". What is taking place in opals, is not dispersion, but iridescence. We divide all opals (a huge group of gems) into precious and common, based on whether they have color play, or not, respectively. (http://www.bwsmigel.info/lesson6/de.optical.phenomena.html)
In the 1960's, the reason of the color play was discovered with the aid of the electron microscope, where it was determined that Opal is composed of tiny silica spheres that can be arranged in an orderly pattern. This diffracts the light entering the stone into the spectral colors. A light wave diffracted through the Opal causes a color sheen or scintillation in the stone. The density and pattern of the aligned silica spheres are responsible for the different colors refracted in the Opal. Common Opal lacks this effect, since its spheres are disordered or too compact to permit the light from refracting.
A condition called crazing affects certain Opals, causing them to form internal and external cracks. Crazing is a particularly interesting phenomenon, since it lacks consistency and is unpredictable. Although it can occur at random, it usually strikes when an Opal removed from damp conditions is allowed to dry too quickly, or when an opal is exposed to sudden intense light (or a combination of these factors). Crazing may also take place when an opal is subject to vibration, as during the cutting and polishing of a specimen. The severity of the crazing and the time it takes to "craze" varies among specimens. The origin of the specimen is often a determining factor to its resistance to crazing. A very gradual drying process over months or even years can in some cases effectively stabilize the stone and allow it to be cut and polished with a substantially reduced risk of crazing.
Uncut Opals are often stored in water; this reduces the chance of crazing. Once a specimen is taken out of the water its susceptibility increases. Opal stored in water should not be taken out of the water for more than several minutes at a time. Cutting or polishing Opals, especially Opals from localities notorious for crazing, is a risky process; it is a matter of chance if the Opals will craze or not. To further protect Opals from crazing, they should not be washed with chemicals or detergents and should not be subject to sudden changes in temperature or lighting. (http://www.minerals.net/mineral/opal.aspx)
Tourmaline
The name comes from the Sinhalese words tura mali, which mean "stone of mixed colors." Tourmaline is not one mineral, but a fairly complex group of minerals with different chemical compositions and physical properties. Certain trace elements produce distinct colors, and many resulting varieties have their own names:
- Schorl or black tourmaline is rich in iron, which causes dark shades from deep brown to bluish-black. This variety makes up 95 percent of all tourmaline, though most of it isn’t gem-quality. Schorl, in particular, is said to have protective powers against harmful radiation, toxins and anxiety.
- Dravite or brown tourmaline is rich in magnesium, which causes colors ranging from brown to yellow. It’s named for the Drave District of Carinthina (now Slovenia) where it’s found.
- Elbaite offers the widest range of gem-quality tourmaline colors, due to lithium traces combined with other coloring elements:
- Rubellite or red tourmaline is caused by manganese; but if the color becomes less vibrant under different light sources, it may be called pink tourmaline. Indicolite or blue tourmaline can appear purplish blue or bluish green, depending on the amount of iron and titanium.
- Verdelite or green tourmaline can resemble emerald, but if its color is caused by chrome and vanadium, it’s called a chrome tourmaline.
- Paraíba tourmaline is a vividly colored purplish or greenish blue variety found in Paraíba, Brazil. It’s the most recently discovered, and because of its desirably intense colors, it’s one of the most valuable.
- Achroite or colorless tourmaline is rare.
- Parti-colored tourmaline displays more than one color, due to chemical fluctuations during crystallization. A common color combination is green and pink. These are often cut in slices to reveal a red center surrounded by a green rim, earning the name “watermelon tourmaline.”
Tourmaline is mined in Brazil, Sri Lanka, Nigeria, Mozambique, Madagascar, Afghanistan, Pakistan and the U.S.—mainly Maine and California. Its wide range of color options makes it a very desirable gemstone.
Shared from:
https://www.americangemsociety.org/page/octoberbirthstone
https://www.americangemsociety.org/page/octoberbirthstone
**All postings including both informational text and photographs are the property of DG Designs Jewelry and Supply and subject to copy-write standards. I will more than likely let others use or share from my blog as long as I get an email asking me "pretty please with sugar on top" first.**
December Birthstones
There are actually 3 gemstones associated with the month of December; Zircon, Tanzanite and Turquoise. I will concentrate on Turquoise because it is the most widely accepted and used December birthstone.
TURQUOISE
The name turquoise is derived from the French word turquois meaning "Turkish". Silk Road traders first introduced turquoise to Europe when they began bringing the mineral towards Europe through Turkey during the 17th century from mines located in Persia. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique and varied color range.
Rulers of Ancient Egypt, the Aztecs, Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China have all been adorned with articles of turquoise and shared common beliefs that the stone afforded many qualities of protection and good fortune. For thousands of years Persians used turquoise extensively to adorn mosques and buildings of importance as well as articles of clothing and horse bridles. Persian turquoise was often carved into objects and inlaid with gold. They wore turquoise around their neck or wrists as protection against unnatural death.
Necklace found in the tomb of King Tutankhamen
One of the turquoise domes at the Shah's Mosque in Isfahan, Iran. Also known as the Royal Mosque
The southwestern tribes of Native Americans such as the Pueblo, Navajo and Apache cherished turquoise for amuletic uses in items to adorn their horses, arrows and pendants and consider the stone to be sacred. In contemporary Western use, turquoise is most often cut into cabachons, set in silver rings, bracelets and necklaces, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. Lesser material may be carved into fetishes, such as those crafted by the Zuni. The Navajo tribe began using silver to make jewelry around 1850 when Navajo artist Atsidi Saani learned blacksmithing at Fort Defiance in Arizona. It was also about the time that the tribe was becoming less nomadic and they began sharing and learning different techniques withing the tribe. The Navajo are without a doubt the leader in sterling silver jewelry work and continue to use the "sky stone" as a feature of their work. While strong sky blues remain superior in value, mottled green and yellowish material is popular with artisans.
Examples of Navajo Turquoise and silver jewelry. (I tried to find the original publisher/photographer of this photo but as of today I am still researching)
Turquoise can come in different shades of blue or green, and is commonly veined or included with brown or black oxides or a sandstone base. Some prefer this color veining, while others prefer a solid-colored stone. Turquoise may occasionally also be mixed together with green Malachite or Chrysocolla, causing blue and green mottled gemstones. The picture below is a great representation of the color variation that can be found in one mine alone.
Rough nuggets from the McGinness Mine in Austin, Nevada . Blue and green cabochons showing spiderweb, Bunker Hill Mine, Royston, Nevada.
Source: This photo taken by Chris Ralph of http://nevada-outback-gems.
Source: This photo taken by Chris Ralph of http://nevada-outback-gems.
Some of my all time favorite examples of turquoise inlay are the articles recovered from the ancient ruins of the Aztec, Mayan and Inca civilizations. The Aztecs created ceremonial objects with mosaic inlays of turquoise, gold, jade and shells like knives, shields, masks and even implanted turquoise into the teeth of royalty and other members of high importance.
Turquoise mosaic masks from ancient Mayan and Inca civilizations
Double Headed Serpent 15th to 16th century Aztec Turquoise mosaic ear adornment from Inca civilization
Turquoise dental inlay for Maya nobility and those of high ranking
Turquoise is a porous gemstone and is thus easily dyed. The dying is done to enhance the blue from more greenish or mottled stones. Dyed stones can eventually wear off their enhanced colors over the years, or when exposed to certain chemicals or solutions. The luster of Turquoise is often dull, and it is therefore very common for certain dealers to impregnate or coat the Turquoise with a a plastic lubricant or wax to enhance its luster. Due to the common practice of dying and enhancing Turquoise, this gemstone especially should only be purchased from reputable dealers who fully disclose all information.
The porous nature of Turquoise makes it more easily affected by oils and cleaners. Because of this, Turquoise gemstones should not be washed with anything other than water. Turquoise is also a relatively soft gemstone, and extra care should be exercised to prevent it from scratching.
Side note: After an incident at the last show where I was a vendor I decided to research the fluorescence properties of various stones and learned that under longwave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays. (https://en.wikipedia.
Chemical Formula CuAl6(PO4)4(OH)8 • 4H2O
Color Blue, Green, Multicolored
Hardness 5 - 6
Crystal System Triclinic (3 axes of different lengths without right angles to each other)
Transparency Opaque
Luster Waxy
Cleavage None
Mineral Class Turquoise
The porous nature of Turquoise makes it more easily affected by oils and cleaners. Because of this, Turquoise gemstones should not be washed with anything other than water. Turquoise is also a relatively soft gemstone, and extra care should be exercised to prevent it from scratching.
Side note: After an incident at the last show where I was a vendor I decided to research the fluorescence properties of various stones and learned that under longwave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays. (https://en.wikipedia.
Chemical Formula CuAl6(PO4)4(OH)8 • 4H2O
Color Blue, Green, Multicolored
Hardness 5 - 6
Crystal System Triclinic (3 axes of different lengths without right angles to each other)
Transparency Opaque
Luster Waxy
Cleavage None
Mineral Class Turquoise
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