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Gemstone for the month of October: Opal
Congratulations to our friends who celebrate their birthday this month.
Lucky you! Your birthstone comes in all colours, there is always an opal that suits you.
In ancient Roman times, opal was the symbol of love and hope and was given the name opalus which meant precious stone. In 75 AD, the Roman scientist Pliny wrote that opal encompassed the red of ruby, the green of emerald, the blue of sapphire, the yellow of topaz and the purple of amethyst. Legends in Arabia say that opal falls from heaven on earth in flashes of lightning. In Europe opal is considered as a symbol of hope, truth and purity.
Once, opal was thought to preserve the life and the colour of blond hair!
A rough thin layer of opal in it host rock, a sandstone. The square cut stone comes from this rough rock
Opal is a unique gemstone which displays flashing rainbow colours, it plays with colour, like a natural kaleidoscope!
How are opals formed?
Did you know that opals are the product of rainwater?
Precious opal formed when seasonal rainwater drenched the dry ground in, for instance, the Australian desert.
The water soaked deep into the ancient rock and carried silica along its journey. Silica is a compound of silicon and oxygen. The silica rich solution now fills up the fractures and cavities in the rock.
In the summer season the water evaporates the silica is left and the gem opal deposit forms. This process takes place over a period of millions of years!
What are opals made of?
With a magnification of more than 30.000X, scientist have discovered that the play of colour of precious opal is caused by diffraction of white light by silica spheres with evenly spaced gaps. Every opal is a unique creation of nature, there are a few main factors that determine the quality of opal: colour, pattern, inclusions and transparency.
Diffraction of white light by silica spheres, white light breaks up into the rainbow colours
Opal comes in all spectrum colours. A precious opal might show only one colour, two or three colours, and all colours of the rainbow. Opal may also display a background colour which is caused by impurities within the spheres of silica.
A highly desirable black opal with a lot of red play of colour
Clarity and transparency
The clarity of opal can range from completely transparent to opaque. With opal, clarity is the degree of transparency and freedom from inclusions. There are different levels of clarity for opal types. Crystal opal, for example, is admired for its transparency, on the other hand, black opal is highly prized for its black background. The value of an opal can be lowered by a cloudy or milky background. It makes the stone less attractive and less stable.
A crystal opal with play of colour in a harlequin pattern
This is the arrangement of the play of colour of an opal. Just like the shapes of the clouds in the sky, it takes many forms.
Some terms to describe the play of colour patterns are
- Pinfire or pinpoint: small, closely set patches or points of colour
- Harlequin or mosaic: angular and broad patches of colour
- Flame: sweeping reddish bands or streaks that shoot across the stone
- Peacock: mainly blue and green
Opal connoisseurs prefer the large colour patches over the tiny dots. Opals with a bright colour, no matter what pattern, are always the most valuable.
This black opal shows a harlequin pattern with a lot of red, blue and green play of colour
Fire opal has a transparent to translucent yellow, orange or red background colour which is probably caused by iron impurities. The best quality fire opal has a uniform colour throughout the gem.
A spectacular fire opal of 132 carats
Where are opals found?
The best-known source of opal is Australia, about 90% of the world’s opal supply comes from this country. Other sources of opal are: Ethiopia, Brazil, Honduras, and Mexico.
Mexico is the major source of fire opal, since 1870 there mining activities in the state of Querétaro and the city of Magdalena in Sonora.
Care and cleaning
Warm soapy water is always safe.
Do not expose your opal to extreme light, heat or dryness.
Opal has a low hardness and requires care when wearing