Thursday, 31 December 2009

Ho Ho Ho!

Dear readers one and all,

A Merry Christmas (slightly delayed, but what's a fwe days to a geologist?) and a pre-emptive jolly New Year as well. It should be quite a year, too... it's possible that I'll finish my gallery, and can finally present it to the world (well, Leeds anyway).

The currently bald sheep. Poor thing.

In the spirit of general festivity, what better things to give to one's dear ones than some sparkly things? Diamonds, I hear you ask? Rubies and sapphires? No, don't go giving her ideas. A woolly sheep will do for starters. For, you see, my dear Dr. Sock is a dab hand with the old knitting needles, and has been threatening to get a sheep for ages. In an attempt to forestall this, I've got her one first, and yes the wool really does grow. Although the poor thing is a touch on the chilly side at the moment... I'll let you know how the fleece grows, and how she gets on with the knitting with it.

For my dad, what better way to get him to take out the geological hammer than with geodes? These wonderful little things are sufficient to assuage anyone's gambling urges, and at the same time... well, they're rocks. Can't say fairer than that.

You see, you can never be sure what's inside a geode until you look. We know how they form, but it's all a bit of pot luck as to whether you have a good one. It all starts with bubbles in lava. Volcanoes erupt because of bubbles - it's the air pockets that makes the magma light enough to rise up to the surface. Once it gets there, the poor lava finds that it should have brought an extra woolly jumper, and promptly freezes - trapping bubbles in mid-escape.

Over the years (and lots of them), water filters through cracks, gets heated by the volcano, and deep underground, strange things begin to happen. First, bits of the solid lava start to dissolve (especially the quartz). Some time later, when the water cools down in the crack and the bubbles, it starts to de-dissolve... and hey presto, a geode! All ready for the smashing.

What you find when you crack them open are normally layers of crystals (often coloured quartz) growing in from the edges. Sometimes the crystals are too small to see, and you just have coloured bands of chalcedony (agate) instead. The best ones are hollow in the centre, so you can see the crystal shapes pointing inwards, but quite often they're solid. The colours are due to other things dissolved in the water, which formed impurities in the growing crystals - iron, magnesium, uranium, kryptonite...

So how did he do? Well... it could have been worse. The first two were virtually solid, but you can at least see layers of blue-grey chalcedony, surrounded by less pure brown stuff. It looks like the second geode has been cracked while forming, with the clearer bit in the middle forming later. The third one was better - almost clear blue-grey chalcedony with a hollow centre coated in tiny quartz crystals. Not bad for a beginner.
Of course, to get the more interesting crystals is more of a challenge. Quartz is all very well, and it's vital for our technology (that's where silicon comes from) - but the stuff in these geodes just isn't pure enough to be useful. The only reason for collecting these geodes is because they look pretty. There's nothing wrong with that, of course - it's how most people start getting interested in minerals. On the other hand, it's not going to solve all humanity's problems. You need lots of different minerals to do that...

Wednesday, 23 December 2009

Sal Mirabilis!

Mornin' all.
For those who can't sleep for worrying about what's going to turn up in the green gloop, here's a quick note to let you know. After the first day, long clear needles started appearing on the string - up to 2 cm long. As soon as I got the camera out, though, they'd all vanished!

This does happen, sometimes - things crystallise, and then dissolve again. This time, though, it was more mundane - the crystals had got too big and fallen off!

So, a quick decant later, and here they are, growing together in the bottom of the beaker:

The green is just colouring from the solution itself, and don't worry about the brown blob on the right - that's the remains of a paperclip I dropped in for fun. As I might have said, it's good stuff, this!

Now, I know you're dying to know what this is, so here you go:

The crystals have a parallelogram-shaped end that slopes to one side, but are otherwise long thin prisms. Of the possibilities from what went into the gunk (sodium chloride, copper sulphate, and a bit of aluminium) this can only be...

(hydrated sodium sulphate, Na2SO4.10H2O)

Nice name for a very nice little crystal. Now, since we've taken some sodium and sulphate ions out, there should be a bit of copper chloride waiting for us after Christmas... that'll be fun! Unfortunately it's doomed to crumble into a white powder once it loses water. But it does make an exceedingly good purgative, as discovered by Glauber in 1645... and hence the name! Miraculous indeed! Any volunteers?
Have a lovely sparkly holiday, and may Santa bring you lots of obscure mineral growths that you've never seen before. If he doesn't, I suggest checking his beard for them. That's where I keep mine.

Tuesday, 22 December 2009

Latest experiments!

Dear Reader,

I never get tired of growing my own crystals. Many of you will have grown crystal gardens in your childhood days, perhaps from salt or copper sulphate. You can buy kits, of course, to help with this, but a lot of them cheat by making chemical reactions happen in front of your eyes. Those ones really don't tell us much about natural minerals...

No, the best methods are those that let the crystals grow naturally, as they want to. We merely... encourage them. Perhaps with an oven, if we need to. Actually, I must confess to getting bored as well, so I'll speed them up when I can. I don't think it makes much difference to the result, though - it all comes out in the wash (unless you're using potassium cyanoferrate - that stains like anything!).

I should probably explain how to do it, too. Take lots of whatever you want to grow, dissolve it in water, and let it evaporate. That's about it, really.

So, guess what? I've got hold of some boric acid, copper sulphate, and aluminium sulphate. They're all nice crystals, if a little toxic. I make very sure not to get them mixed up with my muesli, I can tell you. As long as you don't eat/drink/inhale/spill them, they're pretty harmless. Copper sulphate gives you a gorgeous blue colour when you dissolve it in water, too. Here's some I've started to make at home.

Now, I read somewhere recently that if you dissolve copper sulphate and salt (sodium chloride)together, you get a really nasty liquid that's used to etch metal. I've not heard what crystals you get when it evaporates, though. Of course, it's far too dangerous to do this at the museum - they wouldn't like that at all. So I've done it in my kitchen instead. :)

For some reason it turns a wonderful dark green colour. That's always a bad sign - I mean, would you drink something that looks like that? Then, of course, I had to test the alleged metal-etching powers of the mixture... does it live up to expectations..?

Here's what happens when you dunk a bit of scrunched-up aluminium foil in it. Note the fizzing. I'm not sure what gas was coming off, but it was probably chlorine or hydrogen, so I'm not going to get too close...

On the right is the aluminium after 20 seconds of dunking. Good, eh? Any guesses as to which crystals will end up growing in that horrible gloop first? Sodium sulphate? Copper chloride? Just some weird green gloopy stuff?

You'll just have to come back and find out. I honestly haven't the faintest idea. But when I do know, I'll tell you. Along with revealing what's in those other beakers...