Science Interviews


Sun, 27th Apr 2008

Sparkling Science

Ian Mercer, Gemological Association of Great Britain

Listen Now    Download as mp3 from the show The Sparkling Science of Gemstones

Chris - Ian Mercer joins us now in the studio from the Gemological association of Great Britain. Heís here to tell us more about it.  Hello Ian.

Ian - Hello.

Helen - Thanks for joining us. Now first off what is it that makes a gem a gem and how do we know that one is a gem stone?

DiamondsIan - Well, when you look at a gemstone and you think, ďThatís really beautiful. That really appeals to me and Iíll get my husband to spend lots of money on it,Ē well thatís one of the attributes of gems. Also, they have to last quite a while, donít they? So they have to be a bit durable or hopefully, very durable. I guess pearls are less durable and diamonds are less durable but they are both gemstones. Itís a bit variable.

Helen - Itís not a strict definition of a certain chemical compound or anything like that?

Ian - Itís not that strict and depends on those particular factors and also it helps if theyíre rare as well. Of course, it is quite rare to get beautiful big crystals. Therefore thatís something else that people will pay for and then value. Also theyíve got to be acceptable, donít they? Theyíve got to appeal to your fashion and appeal to your community or perhaps not come from living elephants and things like that. How acceptable are they? That really also is a factor. Really, I guess in the end itís something somebody pays a lot of money for.

Helen - Excellent. I have here in front of me in the studio a large lump of, what I think is very beautiful. Chris, I donít know if you agree?

Chris - Wow, is that yours?

Helen - No! <laughs> Itís just something I brought with me(!)

Chris - Is this your engagement ring?

Helen - No, Ian brought this in. Itís a lump of Ė Iíll describe it Ė raw crystals, I suppose. Itís about the size of my hand, slightly pale blue in colour with some straight edges. What am I looking at, Ian?

Ian - Youíre looking at aquamarine crystals. They are beautiful gem quality crystals as grown in the Earth, very hot, underneath an area where there are volcanoes. Thatís just as it forms, hasnít been cut and polished.

AquamarineChris - Thatís the size of Helenís fist, how much would that be worth? Not that Iím thinking of nicking it or anythingÖ

Ian - I would guess you could spend something like one hundred pounds on a group of crystals like that.

Chris - Why are they one hundred quid but a diamond that size would be unfeasibly expensive?

Ian - Itís partly the rarity value thatís really, how many diamonds do you get on the Earthís surface? Very few. How many big diamonds? Almost vanishingly few.

Helen - Whatís this made out of?

Ian - That is aluminium, beryllium silicate. Itís got beryllium in it which is a strange, rather poisonous metal but these crystals are not poisonous. Itís fairly rare and itís a little bit rarer when itís that beautiful blue. Itís rarer still if itís in big crystals which are suitable for cutting. Of course, you can only cut a lovely gemstone out of a lovely crystal. Youíve gotta start with good to get good.

Chris - Chemically speaking, what actually are gemstones? What chemicals do you find in say, rubies and sapphires and emeralds and things?

Ian - Well, many of them are what we call silicates: a little silicon atom with four great big oxygen atoms around it. If you get those which are four cornered units, tetrahedral, they all link together often with metals and that makes up a nice silicate structure. We think of those as minerals or artificial crystals made as silicates. If those atoms come together really well, perfectly Ė nice orderly arrangement Ė then you get a nice crystal. You mentioned ruby and sapphire, those are oxides, theyíre relatively simple. Thatís corundum. Ruby and sapphire are both the same mineral, called corundum. If you have non-gem quality corundum as a sort of sand thatís what many people think of as emery which is use for grinding.

Chris - Sand paper?

Ian - Yes, emery paper.

Chris - Itís aluminium, isnít it?

Ian - Thatís aluminium oxide, yes.

Chris - Why is a ruby such a gorgeous red colour and itís aluminium oxide? A sapphire is that gorgeous blue colour and itís aluminium oxide. Whatís going on?

Ian - Whatís going on is impurities. You might think, ďWell, how can you call it impure if itís so beautiful?Ē Well, they are metals which get trapped into that structure of aluminium oxide. In ruby itís chromium. In blue sapphire itís iron and titanium and there are many colours of sapphire, in fact. Many people donít realise sapphire could be any colour.

Helen - Iíve got a lovely blue one actually. Iíve got four on my finger which I rather like. You mention volcanoes. Is that where we find all of these gemstones? Is that where theyíre all formed?

Ian - Many are in volcanic districts. Strangely, those beautiful aquamarine crystals occurred in pockets around granite and granite when itís molten is a bit like porridge. It works its way up towards the Earthís surface. If it crystallises out nice and quickly around the edge of the granite then weíve get those lovely big crystals. If it reaches the Earthís surface it forms terrible volcanoes, the most awful dangerous volcanoes ever. Luckily, most of it doesnít get to the surface. The stuff that stays down there might form gemstones.

Chris - How do we know where to look for different gemstones? In other words, because they require different conditions Ė quite specialist conditions to form Ė does that mean that there are hotspots for different types of gemstones around the planetís surface?

Cut RubyIan - There are hotspots. Yes. The type of deposit that forms that aquamarine is called a pegmatite and those are prevalent in certain places such as Madagascar, the Ukraine, Brazil, certain states of America and where there are past or present volcanoes.

Chris - If you havenít got a volcanoes there now but you did in the past, that means there presumably a hotspot there for finding things because those conditions exited there once if not today.

Ian - If thereís the right type of rock, right type of volcanic province, yes. Thatís the place that geologists or gem prospectors are going to look. Theyíre clues.

Helen - You touched already a little bit on rarity and what it is that we like. Am I right that in fact engagement rings: that rubies used to be the ones that people wanted because red colour was romantic, it was the colour of roses and hearts and love and things? It was only later that we were persuade that diamonds were a girlís best friend? I donít know if thatís a story I picked up from somewhere.

Ian - Well, my wifeís engagement ring is ruby. What can I say?

Helen - Wonderful.

Chris - What does a gemologist give to his wife on their engagement? Now thereís a question!


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