Thursday, 19 March 2009

Mother-of-pearl Day

Ammonite fossils sometimes show a mother-of-pearl like layer where the aragonite of the original shell has not changed to calcite, as usually happens. Light reflecting from the thin layers of aragonite undergoes an interference which leads to a beautiful spectrum of colour display.

Ammonites from Majunga in Madagascar can show this effect and those of a South Dakota locality, and there are some Somerset ammonites which can display fine colour too, but by far the best examples come from Placenticeras ammonites in 70 million year old rocks in Alberta, Canada. Here the stone is called ammolite (among other names) and the better grades of ammolite show a fantastically intense, opal-like colour.

Colour ranges across the spectrum, but greens and reds are most common. The purply-blues are rare, and fetch a bit more money. The highest grade gems can be pretty expensive, but it is possible to get nice colour at a reasonable price. Complete ammonites can be found, though they are rare and can take hundreds of hours of painstaking preparation to reveal the colour fully. Needless to say, the ammonites cost tens of thousands of dollars.

Ammolite has been officially classified as a gemstone, though quite what that means I don't know. Nobody's officially classified me as anything. Something to do with grading? Marketing? What I do know is that it looks great. It's one of my favourite stones. I try not to take stones home, but with ammolite I find it very difficult to part with some pieces. I buy mine from a good friend, who collects, cuts and polishes it himself. Not many people are allowed to collect the material, and it's also very difficult to actually find it. Can be dangerous, too - the best stuff is found on the steep, scree covered banks of a torrential river, accessible only for a short period of the year. A large part of the formation is found on a Kainah tribal reservation, and permission to collect is controlled.

The Blackfeet consider the stone to help with the buffalo hunt and call it buffalo stone. There aren't many buffalo near where I live, but I may try it out on some cows. I won't actually hunt them, though. Maybe just sneak up on them.

I've been selling ammolite in the shop for a decade now, and people love it. It took me a while to get round to selling jewellery, but now it's a jewellery line that is memorably different and it's been doing well. This year I picked out a few pendants but also got a bunch of pieces that I will get made into pendants and rings. It takes a bit of time to get them done that way, but is worth doing.

Thought as it was Mothers Day this weekend, I'd pick a gem as a theme today...

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