This is a 15.16 carat Yowah Boulder Opal, measuring as a 19 X 12.8 X 6.8 mm freeform cabochon, its matrix is brown coloured sandstone.  Boulder opal has a hardness of 5 - 5.5 on Mohs' hardness scale.  Boulder opals are amorphous, the diffraction pattern displaying as a broad diffuse band, consisting of a fine layer of natural opal which has formed naturally with ironstone rock.  

Like other precious opal, there are many varieties of boulder opal defined on body colour, play of colour, and patterns.  Its origin is Queensland, Australia. It has had no heating or treatments. It has only been cut and shaped into an oval & the surface has been buffed. This opal colour is in varying shades of  brown and tan with blue opal distributed through out. 

There are two main forms of opal recognized - precious opal and common opal.  That division is based on the presence or absence of the play of colours.  Precious opal exhibit the characteristic play of spectral colours.  Common opal is mostly opaque and shows no play of colours.  Most opal is common - precious opal showing brilliant spectral colours is comparatively rare.  This opal is the rare precious opal.  Precious opal is a highly sought after gemstone.  The best opal are valued by their play of colour and then secondly by their size.   

Opals are a hardened gel of hydrated silica.  Not only do precious opals have play of color, they can be categorized by pattern of colours.  There is a whole range of patterns differentiated in the various types.  This is a sandstone opal.  It is a dark brown, ferruginous sandstone impregnated with solid opal of various shades.  The sandstone opal is formed by replacement of the matrix of the sandstone and is found impregnating the sandstone.  It is not necessarily the size of the Yowah Opal that makes it valuable but also the amount of opal, the colour & the pattern.

The formation of opals began some 50 - 65 million years ago dating back to the Cretaceous period when dinosaurs roamed the Earth.  A second weathering event approximately 25 million years ago formed the second stage in the formation of the opal.  Geological processes of erosion, collection and precipitate leaching, convergence and deposition yielded the final present day opal.

At first appearance, the gem may look like a doublet or triplet, where layers of material are glued together.  It is not a glued together doublet or triplet.  My boulder opals are cut and polished with the opal veneer exposed, leaving the natural ironstone as backing.  The combination of the ironstone boulder and the opal is perfect for jewelry, and it does not have to be set in silver or gold for them to be durable, strong and long lasting.  As a natural gemstone, there are no special care instructions, treat boulder opals as you would any other gemstone.  Yowah Boulder Opals are care free & easy to maintain.  You may even oil it occasionally to bring out its highlight and pattern.

The Yowah Boulder Opal has a double glue process to adhere the sterling silver paddle bail. The necklace includes a 20 inch Italian sterling silver diamond cut curb chain, .85 mm thick, with a lobster claw clasp.  Everyone has to check their chain size before ordering.  This is to assure a comfortable fit.  A curb chain is made of uniformly sized oval or round links that have been twisted and cut to lie flat along a surface.  A diamond cut refers to the finish added to the edges of the chain.  Manufacturers cut small grooves into the metal edges resulting in a brighter more sparkling appearance compared to the chain having uncut edges.  The cuts on this width of chain are not visible to the naked eye, but the effect is still present.

I will be including the original item description with pictures from the seller of the boulder opal to me which will authenticate it's pedigree and origin.  Returns will not be accepted without the item description.  The description is the original and it can not be replaced.  This Boulder opal is 5 - 5.5 on Mohs' scale of hardness and can get scratched by your harder gemstones.  So keep it in the box when not wearing to keep it in good shape, or at least kept inside the resealable plastic bag.

Inside the gift box, I am including a 1" X 1" anti-tarnish tab.  This is the same technology used by NASA, The British Royal Mint, The Guggenheim Museum and jewelry manufacturers worldwide.  The tab provides protection from tarnish for up to 12 months.  It does not leave deposits on items it protects.  It is non-toxic, non-abrasive, and will not scratch or harm metals or gemstones.  Place strips in jewelry cases, storage bags or boxes.  Each tab protects up to 30 cubic inches of container space.

My jewelry is handmade by me and each set contains hand selected gemstones which must meet my high standards.  I purchase my material from reputable dealers from around the world, usually certified sellers.  The jewelry arrives in a gift box, which I recommend keeping in for storage. 

I am always happy to answer your questions Take a look at my other listings in Meet the Seller information, view Sellers Other Items and eBay will create a list for you.  

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