Opal, from the Greek wording, “Opallos”, meaning ‘to see a change (of color)’, and is a non-crystalline formation of a silica gel substance unique to opal. Millions and millions of years ago, this opal gel seeped into crevices and cracks in the sedimentary strata formations. Through millions of years of time and nature’s natural heating and molding processes, the opal gel hardened. Today what may be found in the form of brilliant solid opals.

The Queen of Gems and the fifth gemstone, opal is set apart from other gems because of its unique characteristic appearance, shining sensational sparkling prismatic colors that roll and flash as you turn the opal. No two opals are exactly the same - ever!

Where Is Opal Found?

Australia is the world’s greatest producer of precious opal. Over 95% of the world’s commercial opal are dug from the desolate outback, where it was formed during the Tertiary period of some 15 to 30 million years ago. The history of Australian opal started as late as 1849 at a cattle station called Tarrawilla, near Angaston some 80 km outside Adelaide.

However, opal was first commercially mined at Listowel Downs, near Adavale, Queensland in 1875. This was followed by the discovery of light opal at White Cliffs, NSW in 1890, where the population exceeded 30,000 in its heyday. There is little opal mined there today.

The world famous black opal field of Lightning Ridge, NSW was discovered in 1903 and is still producing many beautiful gems. The discovery of light opal in 1915 made famous the name of one of the most hostile and remote places on the Australian continent - Coober Pedy.

The Different Varieties Of Opal

Opal is found in many different varieties and sub groups. Less than 5% of all opal constitutes precious opal, and of that only 5% is true gem quality. This rarity is much greater than is generally appreciated, as the annual production of precious opal is infinitesimal compared to that of other gemstones such as diamonds. Most opal found has little or no color play - this type is known as “potch”.

BLACK OPAL is the rarest and most valuable type. It is generally found as a bar (or bars) of various colors forming natural water horizontals in dark gray to black “potch nobbies” or “nodules”. Few realize that 99.9% of the world’s supply of this radiant, dark lustrous gem is mined at only two tiny pinpoints on the globe - Lightning Ridge and Mintabie.

BOULDER BLACK OPAL is a special type of opal found mostly in central Queensland. It is a curious formation of silica, which has filled the cracks and crevices in light and dark brown ironstone boulders. Invariably stones from Queensland are cut with the natural host rock (ironstone) left on the back.

LIGHT OPAL (sometimes referred to as “White Opal”) is not quite as rare as the black varieties, but is nevertheless distinguished by lively color play. As the name suggests, the stone ranges from transparent, translucent to opaque with a creamy hue, displaying soft pastel shades of color The “crystal” translucent type is vibrant with shafts of color in intricate pattern variations. A rare formation of “cloudy white” porous

MATRIX OPAL from Andamooka can be treated by soaking in a sugar solution and then boiling in sulphuric acid to deposit carbon in the pore spaces. The black body color thus produced enhances the play of colors, resembling a natural black opal. However, the dividing pattern lines are not as sharply defined as in a natural black opal. The surface penetration rarely exceeds one millimeter.

The Australian Opal Deposits and Opal Fields

OPAL SOLIDS, DOUBLETS AND TRIPLETS

Australian opals are the finest in the world. They have tremendous investment potential and are one of the few gemstones which have appreciated at a steady rate over the past 30 years. But before you race out and buy one, learn a little about them - how they come and what is available. They fall into three categories: solids, doublets and triplets.

Solids are natural stones which have been cut and polished without being interfered with. Many have a natural potch or iron stone back.

Doublets are usually two pieces of opal cemented together. They are made by cementing a layer of high-grade opal to a dark potch back, which enhances the color For economical reasons, many have thin faces. But domed cabochons made from good quality crystal opal, do in many cases, resemble fine quality black opal, which is due to the partial absorption of light by the black back. Their value is only a fraction of that of gem quality solid stones. Though not always encouraged by the trade as an investment stone, the better pieces do bring a reasonable price and are certainly worthy of a place in any good gem collection.

Triplets are doublets with clear domed caps cemented to their faces. The hardness of the cap used may vary from glass to quartz, depending on the quality of the opal. The dome cap protects the opal and magnifies the color and pattern, greatly enhancing the overall appearance.

OPAL FACTS, MYTHS AND GEOLOGY OF OPALS

Here are a few facts, myths and geology about that beautiful opal you have locked away in your jewel case. Firstly, it is a closely-packed array of millions of spherical particles of amorphous silica, stacked in a three- dimensional grating. Because of the special grating, it is the only gemstone known to man that has the unique ability to diffract white light into all the beautiful colors of the rainbow without the help of impurities. Impurities play no part in creating such beauty, as is the case with many other gemstones. Color is created when light is split by the voids which have been formed between the spheres. The size of the voids controls the angle of light and the color produced. To produce visible color, the spheres must be no smaller than 1500 angstroms for violet, indigo and blue, nor larger than 3500 angstroms for orange and red.

When viewing an opal, the most important factor is the relationship of the light to your eyes. To see opal at its best, the light must be coming directly over your shoulder. If you’re in a room using natural light, always stand with your back to a window or a door. If outdoors, stand with your back to the sun. Reverse these positions and you will be amazed at the change in the quality of the opal. With 96% of the world’s production, Australian opal suffers few of the problems which afflict opal from other parts of the world. This is mainly due to the fact that Australia’s opal has grown under totally different conditions - it is sedimentary, not volcanic.

Myths have grown up around opal - the most common being that you should never let oil or common household products come in contact with your opal while wearing it, as they will cause irreparable damage to the stone. This may be the case with volcanic opal, but not with good quality Australian sedimentary opal. On the other hand, an opal is a quality gem and is not meant for everyday, knockabout wear. Another popular myth is that you should soak your opal every so often in water. Again, if it is good quality Australian opal, you would be wasting your time. If you do go ahead and soak it, you won’t damage or enhance it.

The average Australian opals carry around 6% water, much of which is located up in the tiny voids between the spheres. Every 20,000 layers of spheres is equivalent to the thickness of a fine dot made by a ball-point pen, and requires an electron microscope to see them. Under these conditions the water molecule is held so tight that it is near impossible for them to escape.

A temperature of 60 degrees Celsius is required to start removing water from the first few outer layers of voids, and
to continue to remove it at its zenith rate of evaporation requires a steady temperature rise to 250 degrees. Should you wish to remove all the water from your beautiful opal, then you will need to raise the temperature to 600 degrees plus, for some time.

female rx oil
female rx plus
flomax
florinef
glucophage
glucotrol xl
hoodia gordonii
hoodia patch
human growth agent
imitrex
isoptin
joint formula
kamagra
kamagra oral jelly
lamisil oral
lasix
levitra
lexapro
lioresal
lipitor
liquid rx plus
lopressor
lotensin
mevacor
multi vitamin
neurontin
nexium
nolvadex
norvasc
pamelor
paxil
plavix
pravachol
premium diet patch
prevacid
prilosec
propecia
protonix
retin a
silagra
singulair
soma

Another generally taught myth is the depositing and genesis of Australian opal, most of which occurs in Cretaceous
sedimentary rocks. The local name given them, such as desert sandstone, is dependent upon the area in which they occur, but they all belong to the same families of felspathic sandstone, claystone, siltstone and mudstone, which are said to have been deposited over large areas buy streams and lakes.

Except for volcanic opal, which usually occurs in Tertiary rocks, all the types of opal we have come to know so well are found in these strata. Although the opal is found in the Cretaceous sediments, it is a matter of conjecture as to it’s deposition over millions of years during the Tertiary period. The general teaching is that certain minerals were broken down in the country rock to produce silica at 120 parts per million, and trace elements which were deposited in cavities left by bones, shells and other dissoluble material. These, as well as faults and fractures in the ground, provided pathways for the underground waters to carry the silica down at the end of the weathering period.

Although this is the entrenched theory, with “slight variations” depending on your source of information, it is
fraught with problems which have been deleted from the model to give it credence. There is little doubt that all opal was not deposited in exactly the same manner. So far I have discovered four different ways in which it has been deposited; there may be more. They all have a common denominator in the equation, ionic-exchange. The fact is that opalization is extremely regional and that large beds of impervious barriers are only secondary to opal
formation.

If the only requisite for opalization under the above model were suitable impervious traps, then there would
be massive beds of opal over vast areas. However, as every opal miner knows, this is not the case and all opal is
unpredictable and patchy in the extreme. The reason for the unpredictability is the opal was never deposited in the way we have been taught. Many of the problems relating to the depositing of Australian opal have now been solved, both in the field and the laboratory, showing the theory to be incorrect and that the opal was formed under very special conditions which included a form of ion exchange. In geological terms the opal grew quite quickly, picking up various elements during the process. For instance an analysis of Coober Pedy opal shows the following:

6.1% water [H2O], 1.8% aluminum oxide [AL2O3], 0.8% calcium
oxide [CaO], 0.4% sodium oxide [Na2O], 0.2% hematite [Fe2O3],
0.01% titanium dioxide [TiO2], 0.01% zirconia [ZrO2],
0.05% magnesium oxide [MgO], 0.002% silver oxide [Ag2O]
0.005% manganese oxide [MnO], 0.0008% copper oxide [CuO].

Courtesy of Len Cram. online pharmacy without prescriptionbuy silverbuy detoxbuy italian charmsdownload softwareonline pharmacy no prescriptioncanadian pharmacydownload moviesfarmacia en lineainternet drugstoremovie downloadmexican pharmacybuy gift basketsbuy levitrabuy hoodiaprescription drugsdownload moviebuy dvdcheap auto insurancebuy jewelrybuy jewelry onlinecheap online pharmacybuy alcohol testdownload filmdownload musicdownload mp3prescription drugsbuy notebook batterydownload moviesonline pharmacybuy charmsbuy piercingpiercingflash games onlinebuy propecia onlinesearchpiercingno prescription pharmacyonline pharmacyonline pharmacy no prescriptiondownload moviescanadian pharmacybuy soma onlinebuy carisoprodol onlineitalian charmsindian pharmacybuy viagra onlinegeneric viagra onlinebuy levitra onlinegeneric cialis onlineonline pharmacy without prescriptionno prescription online pharmacytransformers movieeuropean online pharmacyprivate porn moviesbuy phentrimine onlineonline pharmacy no prescriptionbuy jewelry onlinejewelry shopsilver shophealth articlespass a drug testbuy oem softwareeuropean pharmacydvd movies