Minerals in fossils

Dear Readers,

Some of you may have noticed a news story recently about some rather pretty fossils from Morocco. I've been lucky enough to be part of the group working on these things, and now it's been published, I can tell you about them and how minerals are (of course) vital to them being preserved.

We even made the cover - that's what I call fame!

The story goes something like this... Once apon a 542,000,000-years-ago-sort-of-time, there weren't many animals. There were some strange things we call Ediacarans, and at least some of these were genuine animals. Most of them, though, may well have been simpler organisms of unknown types, long since extinct. At precisely this time, though, and for the next twenty million years or so, things started happening in the sea that led to lots of animals, skeletons, and generally complicated things appearing in the fossil record. For those in the know, this was the Cambrian Explosion.

A trilobite. This one is from Wales, rather than Morocco, but these creatures are some of the most iconic critters that emerged during the Cambrian Explosion.

During this time (the Cambrian Period), a wide range of extraordinary creatures evolved, ranging from spectacularly spiky sponges to large arthropod predators such as anomalocarids. We know an extraordinary amount about these animals due to a fluke in the fossil record. For some reason, at this time we have a number of remarkable windows into these ancient ecosystems. The most famous is the Burgess Shale in Canada, but there are others such as the Chengjiang Biota of China, the Sirius Passett of Greenland, and the Emu Bay Shale of Australia. All these sites preserve not just the hard skeletons, but also the 95% of creatures without a mineral skeleton. For example, trilobites are famous fossils with a calcite skeleton that covers the soft parts, and pieces of their skeleton are common in the right age rocks. The legs and other soft parts have no mineral content, though, and these normally rot away completely, along with all the other jointed-legged critters that didn't have the calcite skeleton of trilobites. The Burgess Shale-type faunas have preseved all these lost animals, and shown us what the communities really looked like...

The wonderfully spiky sponge Pirania auraeum -one of a host of survivors from Cambrian times.

There's a twist to this tale, though - they virtually all vanish from the fossil record at the end of the Middle Cambrian. For decades we have wondered whether there was an extinction event that wiped them all out, or whether they carried on into the Ordovician and later periods but have not been preserved. And... well, now we know.

The scenery of the Draa Valley of Morocco, near the edge of the Sahara. Not the place to get your car stuck on a boulder...

The new sites in the Lower and Upper Fezouata Formations of Morocco preserve a wide range of Burgess Shale-type creatures - not the same species, but certainly very similar animals. And the unique thing about the Fezouata fossils is that they're in the Ordovician, some 30 million years after the last examples from anywhere else. They prove that these creatures survived long after they appear to have vanished, and shared the world with animals that appeared in the Ordovician Period. The fauna includes, for example, the earliest known barnacles and horseshoe crabs.

The Ordovician was also an extraordinary time in the history of life, in which animals diversified to an amazing degree. By the end of the Ordovician, there were reefs, corals and even fish; the world would have looked relatively familiar... sort-of (under the water, anyway - there was still virtually nothing on land).

But what about minerals? Well, the question of course is how these soft creatures were preserved, and we think we know roughly what happened. Of course, it all depends on chemical reactions. The fossils are preserved as bright orange or red shapes on green rocks, and that simple fact tells you most of what you want to know. The colouring is due to iron oxides - basically, rust. These rocks are very deeply weathered, so we know that they would have started out as something else - something iron-based - before they rusted.

Cubic crystals of pyrite, starting to go rusty. Leave it in Morocco for another few hundred million years, and it would be a tad bit more rusty...

They couldn't have been pure iron, though - that simply doesn't form in this sort of way. Look really closely, and you find there are a few crystal shapes preserved. The shapes include tiny cubes and octahedra... the tell-tale signature of pyrite.

Pyrite (iron sulphide) is also relatively easy to form chemically. In fact, we know of several other places where pyrite has preserved soft tissue of fossils. In these cases, the pyrite forms because of a group of microbs called sulphate-reducing bacteria. When these anaerobic beasties start eating a carcass, they get their energy from converting sulphates to sulphides. Very rarely, there can be enough of the right sort of iron dissolved in the water that these sulphides react with it to make tiny crystals of pyrite. The crystals end up coating the animal that's rotting away, sometimes just on the surface but sometimes also the internal organs. And that seems to be what's happened here.

Exactly that appears to have happened at some sites in Wales that I work on, as well. In that case, the rocks aren't yet completely weathered, and the pyrite can be seen in X-ray... like so:

An X-radiograph of pyritised beasties from a site in Wales - hydroids and sponges, in this case.

It's rarely quite that simple, though, and there are some specimens that show a range of different minerals apparently being involved. There are 3D worms, for example, that seem to have calcite (calcium carbonate) filling the centre of where the body was, and some sponges with what appears to be a thin sheet of quartz (silicon dioxide) over the soft tissue. The latter is probably because the skeletons of these sponges was made of opal (a type of semi-crystalline silica). There are even different shapes of pyrite crystals preserving different tissue types. There's bound to be more to make of this story as we uncover more and better preserved fossils, but what we know of the original mineralogy is always going to be a little limited... the rocks are so deeply weathered that we'd have to dig a well to find examples with the original crystals still there!

Hmm... might well be worth it...

Looking after pet rocks

Dear all,

It's been a very busy month! As many of you know, because I've met you, I've spent a lot of time running around my gallery making sure that you don't break anything - and that you all enjoy yourselves, of course! I'm sorry I can't be there every minute, but it's been very good to meet all of you that I have, and trying to answer all your fascinating questions. Not so many of the really hard ones, please - how am I to know what minerals there are on planets around alpha centauri? Of course, I've got some experiments planned, but there are always problems with the budget...

I've had a lot of interest in how to look after my pet rocks, so I thought I'd write you a little guide to finding and caring for them. I hope you find it as fulfilling a hobby as I do, but please don't take on the responsibility lightly. A rock is not just for Christmas, you know, and I can't stand the thought of poor neglected pebbles sitting in a dusty corner just because someone has got bored of them.

Any questions or advice wanted, just ask. Good luck... (Especially to the rocks!)

Two of my pet rocks, which Dr. Sock has kindly knitted hats for. The igneous one on the left is clearly delighted with the clolour scheme, whereas the slightly confused sandstone is a little distracted by its nose. Discovering their facial features for the first time can be a source of some confusion for rocks, especially if they had plans to be a model or film star.

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Finding and caring for your Pet Rock

It may come as a surprise to many, but rocks with personalities are all around us. Have you ever had the feeling that the pebbles on the beach are giggling at you? Or that you’re being followed by stones around the garden? Of course, they are extremely shy. Until you get to know them very well indeed, you probably won’t be able to see them moving, or really understand what they’re trying to say. With a little effort, though, you can learn to love the friendly rocks in your neighbourhood, and they can become excellent pets.

Choosing your pet rock
Rocks that might want to become your pet can be found in many places. You will find some subterranean ones burrowing in the soil in your garden, and once they’ve had a good bath, you might find that they become quite beautiful. They may have some rough edges, and sometimes they hide underground through a feeling of shame that they’re not as smoothly polished as other pebbles… but they are often very loyal, and have the most complicated personalities of them all.
For those without a garden of their own, some rather glamorous relatives can be found alongside rivers and by the sea, or from wild places. Of course, it goes without saying that you should never even consider kidnapping a pebble from someone’s garden – they are probably quite happy there, and will pine if taken away. Even taking a pebble from farmland could cause problems – it is sometimes tricky recognising a wild pebble from a free-range one. It is actually illegal to remove pebbles from beaches in most places, so make sure you get permission from the landowner if you want to take one or two to a new home. I’m assuming you’re allowed to find yourself a pebble in the place you’ve chosen, though.

Sometimes there seem to be too many rocks to choose from, especially when you meet the gregarious seaside varieties. When you see a rock that you like, be careful when you pick it up. It often has lots of tiny friends that have come round to visit, and are hiding underneath it. Insects, crabs and other creatures are very fragile, and many of them live underneath the rock; if there are lots of creatures there, put it back gently and look for another. Rocks with such a big circle of friends would be very sadly missed.

Sometimes people are tempted to take more rocks to look after than they can really cope with. For beginners, a small group (two or three) is ideal. One on its own might get lonely, but more than three and you risk them not getting on with each other, especially in a small house. Selecting the stones with the right personalities is difficult but very important. Of course, if you find two or three rocks that have chosen to be together in the wild, you know they’ll be alright at home as well.

What you can do for your rock
Sometimes it is difficult to see the features on your new pet rock. Spend a little while getting to know it before you do anything rash – working out which end is the front, for example, is quite important. Once you’re sure, you can help your rock to see by adding some eyes. Painting them on will work, but sticking some googly ones on is even better, so it can look in different directions when it wants to. Be careful that you put the eyes on the front end, in a sensible position, and that they’re not going to fall off or rub off too easily. Once a pet rock has got itself some eyes, it will miss them if they’re gone, and become depressed. A sad rock is a miserable thing indeed, and you will want to do everything you can to make it feel thoroughly looked after.

Finding the other parts of their face can be harder, but an easy way is to leave a marker pen next to your rock, then give it some peace and quiet. Come back a few hours later, or after a day or two. Be patient – it’s probably nervous. If it likes you, then you may well find that it has drawn on a line where its mouth is (and perhaps a nose as well).

You can tell a lot from the expression it draws. A big grin means that it has settled in already and will make a splendid pet. Don’t be worried if it has a little bit of a frown, or a puzzled sort of expression – these might just be a little grumpy, but are equally lovable once you get to know them. They might well be more intelligent, as well. If you find it has drawn a ferocious snarl with sharp teeth, then you’ve probably picked a bad one. These will never be happily domesticated, and you should return it to the wild before it bites you. Carefully. I’d advise wearing gloves.

Although your pet rock will be comfortable enough without any clothes, those who really want to care for them might wish to knit or sew them a little woolly scarf or hat for the winter months. It certainly isn’t needed in the summer, but is bound to be appreciated in the cold nights.
You then need to think about where to keep it. Many people just let them have the run of the house, and they will certainly enjoy the freedom. Like all pets, though, it is good for them to have a little place to call their own, even if it’s just a corner of the sofa. A tray with sand in will make a seaside pebble feel at home, and a bed of dry grass might be comforting to a garden rock. It is good to have something that will remind them of their previous home – as long as their new home is better, of course!

Many rocks like to have a few simple toys – a marble, a ribbon, that sort of thing. Some will enjoy a little climbing frame, if you have one – but they are often shy about using them when anyone is watching. Don’t expect your rocks to be running around everywhere as soon as you take them home – they’re slow-moving creatures by nature, and take time to get used to a new home. With a bit of thoughtfulness, though, you can cater for anything they might want.

Personalities
You should be aware that many rocks will have different personalities, and often it will depend on what species they are. You must remember that rocks are very, very old, and are extremely patient. They might seem to be a bit slow, but that’s because some of them remember the dinosaurs, and they don’t want to draw attention to themselves.

Assuming you don’t have a bad one (as described above), your pet rock may turn out to be docile, lazy, exuberant, mischievous, or grumpy – it’s hard to guess, and you just have to keep getting to know it to find out. Volcanic rocks are often the most docile – they want a bit of peace, after all the excitement of the volcano. It’s often the sandstones and slates that are most mischievous, and many of them will take great delight in hiding in surprising places. It’s the bouncy metamorphic ones you have to watch out for most, though – they may be small, but they’re very hard, so make sure they have enough to keep them happy, or they may start misbehaving.

It is often useful to keep a little diary of how your new pet is developing, and it will make for fascinating reading for future generations. If, in the end, your pet rock escapes back into the wild, don’t worry too much. It will, I’m sure, remember you fondly, and think of the experience as a grand holiday. Don’t feel sad – it will be quite happy out in the rivers and woods once again, and you can simply go and find a new one...

Eek - they found me!

Dear all,

Cataclysmic times are apon us! My peace and quiet has been shattered! There I was, thinking it was just mice running around in the pipes (or perhaps my pet rocks - they've been escaping again lately, the clever little things), and suddenly they come crashing through the wall! Worse still, the whole thing was caught on security cameras, and now they're putting it up on YouTube! Can you believe the impudence?

I don't mind telling you, it was quite a shock. For them, I mean. I like to think that they were all over-awed by the sheer splendour of the gallery before them... but that's doesn't quite explain the expressions of horror, so perhaps that's not it.



Anyhow, over the past week, they've been taping over the edges, sticking things over the shelves to keep my hands off, and making all sorts of ridiculous pictures of me. Some of them were even videos, which was quite fun - perhaps I should become a film star instead? I bet I could set box office records... but perhaps not the ones they're hoping for.

After all the excitement, the good news is that they're letting you all in to see the place. At least, I think it's good news. I really wasn't ready yet - a few more months of experiments, and perhaps there would have been all sorts of wonders... but still, I do have lots to show you. We'll have to see how the crystal gardens develop, and I'll need help with my cave painting project. Believe it or not, it's free as well, so you can come back as often as you like. I suppose they thought it wouldn't really be fair to charge entry for something like this... although if we get lots of donations, then I might be able to add extra experiments - and you'd like that, wouldn't you? You can make suggestions on the feedback forms as well - I promise I'll read them, and if it's a good idea I might even try it.


You may well see me running in and out of the gallery to check on things, so please feel free to say hello if you do. Actually, if you could remind me about fixing my rock cage, that would be really helpful. And please do keep an eye out for escapees - I know there are loads of them scuttling around the exhibition, and I fear that some of them are getting even further afield.
Two lucky victims - sorry, recipients - of Dr. Sock's hat-making. At least one of them seems happy...

Enough for now. I'm off to recover from the experience of meeting the press. Abnormal service will be resumed shortly. Please come visit me at the Leeds City Museum, and let me know of any requests for strange subjects that I can write about (yes, I'm working on the dissolution one, anonymous!)


Toodle-pip.

In the bleak mid-winter...

Hello all,
There's one type of crystal that's been at the forefront of everyone's mind over recent weeks - at least in the UK. I am, of course, talking about the glorious hexdendritic dihydrogen monoxide. Crystals are normally things you have to go out looking for to find, but not at the moment. You could hardly avoid them, whizzing over your head in powdery ballistic spheroids, or joining forces in a bold attempt to stop the trains going anywhere.
Of course, I'm talking about that delightful thing called snow. When you see satellite photographs showing the entire country covered by a white blanket, you get a sense of the scale of it. Crystals, crystals, everywhere...
So does ice count as a mineral? It seems like a tricky one, at first. According to the International Mineralogical Association's official definition, a mineral is a solid, chemically homogeneous and normally crystalline substance that formed geologically. Well, ice is certainly solid (when it's not melted, of course), and it's certainly a homogeneous crystal... in fact, ice does fit all the criteria.
It turns out that ice is indeed defined as a mineral by the IMA. It could hardly not be, really. If it melted at a couple of hundred degrees, instead of zero, then you'd never think to question it (it wouldn't rain either, of course, and there wouldn't be any oceans, tea, or indeed living things; so you'd probably have better things to not worry about). Where was I? Oh yes: ice. It even forms familiar types of crystal growth... here are some stalactites, for example:

Ok, so snowflakes are a bit weird, though. It's said that every snowflake is unique, and it's probably true... but the shape still follows simple rules. Like apatite, beryl and wurtzite (I like that one!), ice has hexagonal crystal symmetry. It tends to grow more quickly at the tips of the hexagon, though. Each spine often branches repeatedly, leading to the typical snowflake shape:

You can see immediately it's not a random branching pattern, because it's the same on each spine. So what controls it, and why is each one unique? It's all down to the conditions it forms in. When atoms join onto the tip of a crystal, the place they attach to depends on the exact humidity and temperature. Under some conditions, the crystals will form almost perfect hexagons (although I've never seen these myself):

If the temperature is quite cold where they form (-3 to -8C), it's common for all except one or two rays of the crystal to not form at all. I was a bit surprised to find little snowy needles falling on me the other day, so I'm very glad to find out what was happening.

The normal pattern that we see is called a dendrite, from the greek word for tree - it branches. (People often think scientific words are really high-brow, but it's really not true; you just need to look at species names, like Horridonia horridus... scientists really do know how to have a bit of fun when they can get it!) Dendrites are common structures in crystals, whenever it grows mostly in one direction, and occasionally branches. Here's some pyrolusite (manganese dioxide) I found earlier.

Anyway, back to ice. It would be much more obvious that we should think of it as a mineral if we had, say, pebbles of ice in our rivers. Well, if you go to Titan, the moon of Saturn, that's exactly what you get - pebbles and boulders of water ice, in ethane or methane rivers. Water can even form the solid surface of some planetary bodies, and I must confess I'd really like to visit some of them...

Take Europa, for example - a fabulous place. The crust is made of water ice, probably with a deep ocean underneath. Where the crust has cracked, more water has frozen in the gaps, and some of this is coloured brown. What does that mean? Probably that there are minerals dissolved in the ocean, and circulating around with it. And where there are minerals and water, there might be life. A pet rock from Europa would really be something... I wonder if I could keep it in my freezer?

Thanks to NASA for putting these pictures in the public domain. I must go and do some more about putting my exhibition in the public domain too, now. I've just got hold of some flint to try my hand at knapping now... which reminds me, I must go and buy some plasters. Toodle-pip!

Dear Readers,

It's been a busy week! I've been working on my captions (how many bad puns do you think I can get into one exhibition?), and even got our conservator in Leeds to clean up some wonderful Burmantofts pots, without needing too much of a reason. The dragon one is gorgeous. Somehow, I've even persuaded the Temple Newsam curator to lend me a magnificent Chinese jade sculpture - had to be careful not to let on what I was up to, though. I'm getting worried that some of them might be on to me, though. It's the vanishing for weeks on end that's making them suspicious, I reckon. Must work faster, just in case!

Well, what became of the sheep, I hear you ask? I must confess that the vets are not optimistic the poor thing will survive the winter. It appears to have been cruelly treated by callous owners more used to the lucrative sheep showing circuit; worse still, they must have been entering it into the "poodle-sheep" category. Sadly, it wouldn't even have won - I fear that the hairdresser had been at some of my concoctions, and the result is... well, disappointing. Dr. Sock, I hasten to add, is entirely blameless in this case. She told me so, so I suppose I'd better believe her.

Moving swiftly on, I promised an update on the green gloop, and that at least is living up to its billing! Indeed, it's turning more gloopy by the minute, and a delightful brown sludge has appeared at the bottom of the cup. There are definite flakes of copper in it, but beyond that I'm baffled. For a few hours, some more mirabilite crystals appeared on the string, but they took a quick look around and decided that they needed to be somewhere else... I really am intrigued by what is going to happen next!

Soup, anyone?

The string itself is going a bit strange. Normally, string hangs down vertically, like the one in the copper sulphate +boric acid + what used to be aluminium (more of that in a mo) mixture. The one on the right has been in the green gloop, and has opted for a different strategy. It seems to be turning into a copper wire, and I fear it may have plans to plug itself into the mains before taking over the world. Honestly, it was muttering to itself the other day. Or perhaps that was just me.

Ah yes, the copper. Remember that bit of aluminium I was dunking at the beginning? I was getting worried by the buildup of hydrogen in the kitchen, so I transferred it over to the boring old copper sulphate + borax experiment. Much to my relief, it became much more relaxed, but the strange brown colouring still carried on growing. Of course, as some of you have no doubt worked out, the brown stuff is metallic copper. Yep, pure copper metal. I could use it to make a kettle, if I was mad enough. But I'd need quite a bit more. Presumably the dissolved aluminium ions are now swimming around in their nice blue sea...

Copper metal that replaced the aluminium foil - really rather neat!

Since you asked so nicely, I'll let you know what's going on in the pther beakers too. Suagr's in one - but it's boring at the moment - nothing going on at all. The salt is much better - nice little crystals growing happily, but they're probably the easiest of the lot. It would be nice to get some big ones, though. The others are just plain copper sulphate (doing very nicely indeed, thank you!), alum (something is finally starting to happen... but very slowly) and borax (lots of stuff, but it's really not thrilling, even when you zoom in really close. I'm sure I'll get some good crystals one day, though.
Boring old copper sulphate. It is blue, though.

Salt. Nice, eh?

Oh yes, and the mirabilite - it's been drying out well, and is now rather lurid green crust. This should, with any luck, be thenardite - and therefore fluorescent! We'll know soon enough, I promise...

That'll do for now - lots to do still, and there's something else I want to tell you about soon as well!

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...

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...

Mirabilite!

(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.