By Diana Jarrett GG, RMV.
Really, we've wandered up and down the aisles and been in the tents until our eyes are tired. Deep down we wonder: “I've already been here - did I see these things yesterday?”.
Small question. The sensory overload we experience never diminishes. No matter how many years we've been strolling through the world's largest gem and mineral shows. They emerge like some majestic palm tree in the desert every February. So it's hard to explain to someone who has never been there what this behemoth is like. So you have to be there, to use a well-worn adage.
The humble beginning of Tucson gemstone exhibitions
Do you know the origins of this modern mammoth gemstone exhibition? As it turns out, in 1955, a small local club of quirky rock hunters organized a small exhibition of its members' favorite finds. Most displays were confined to open shoeboxes to maintain order.
The first incarnation of the Tucson Gem & Mineral Society was held at a local elementary school. Since then, it has expanded, taking over the entire city and beyond. Various shows start and stop on different dates throughout the month.
“Never despise small beginnings” is the obvious conclusion from this story. But I usually come to another conclusion on my almost annual trip. Vendors from every corner of the globe share their exceptional finds with us. And no matter how many times we have seen these stones, we are once again overwhelmed with the pure wonder of what lies within this land of ours.
Ammonite and sandstone
You have seen the sandstone. I have seen sandstone. But lately I've been coming back to this ancient stone with its fairy tale history. For those for whom this stone is new, it is a mesmerizing wonder to behold.
Sandstone is rightly called a rarity. Any stone that comes from a single source certainly gets this nickname. The organic material is found only in the Bearpaw Formation in Alberta, Canada. Its dazzling colour combinations shimmer with iridescence, presenting patterns that will inspire any designer. It must also be limited because it is a natural organic fossil. When it disappears, it disappears.
The sandstone used in jewellery today was once a sea creature that is now extinct. The fossilized remains of a sea creature left us these remarkable colored shells. As a gemstone material, it hasn't been around for a long time. Its first commercial use in jewellery can be found back in the 1960s. It took some time for it to become established. But in 1981, the World Jewellery Confederation (CIBJO) properly recognised sandstone as a coloured gemstone.
Now this is where it can get a little complicated since we've seen the name sandstone interchangeable with the word ammonite. Let's get these two straight. Ammonites were ancient marine mollusks that became extinct about 65 million years ago. These molluscs of various species can be found all over the world. But only certain species of these mollusks could produce iridescent fossil quality gemstones. And these were found in Alberta, Canada.
Single origin - Small harvest
Even with this limited scope, only about 5% of Alberta's ammonites can yield gem-quality material. This certainly contributes to their rarity.
What to look for
When this ammonite successfully produces gem-quality material, the fossilized shells will be called ammonite. They will consist mainly of aragonite (with other trace elements). Aragonite is the main mineral found in pearls.
But the wide range of shades found in sandstone, their vividly colourful patterns, all play a role in the classification of this material. Most common are the red and green colours. Blues and purples, not so much - so sandstone bearing these shades will be priced higher.
Things like color shift (the change from one hue to another when the stone is moved) and the intensity of the iridescence affect its value. There are other considerations that experienced collectors look for when valuing sandstone stones or jewelry made with this kaleidoscopic gemstone.
As I review my love for this unique precious material, it occurs to me that you might want to look at it with new eyes and help your clients discover a new love from a very ancient source.
Diana Jarrett GG, RMV. Award-winning trade journalist and gemologist Diana Jarrett is a Registered Master Valuer Appraiser and a member of the Association of Independent Jewellery Valuers (AIJV). She is a popular speaker at conferences and trade shows.
Source: southernjewelrynews.com
