Friday at last! We can hear the cheers from here. Unless you are taking part in the Big Hush of course. In which case we hope the newsletter didn’t make too loud a ‘ping’ as it dropped in your Inbox…

The line-up this week:

1. Gimme Five – fascinating facts about …?
2. Scicast Tip of the Week
3. Stump the Scientist: a whiff of a mystery?
4. Activity of the Week: Geodes
5. Mouses at the Ready:  Flipside magazines
6. Noticeboard: FYI
7. Recommended websites of the week
8. The Winners’ Enclosure
9. Joke of the Week

1. Chinese Giant Salamander – it can grow as big as a man!
2. Gardiner's Seychelles frog - grows to just 11mm, the size of a drawing pin
3. Olm - a blind salamander with see-through skin that lives underground. Hunts for its prey by smell and using electric currents and can survive without food for 10 years.
4. Betic midwife toad - evolved over 150 million years ago. The males carry the eggs wrapped around their back legs.
5. Lungless salamanders of Mexico - they don't have lungs but breathe through their skin and mouth lining.

Doesn’t that seem a little salamander-heavy to you?  Perhaps next time we’ll hand them the whole show.  Honestly! Lungless, gigantic, see-through… anything else you’d like to evolve?

Have you got FIVE facts about anything/everything?  Preferably science-based of course (we’re not called Planet Science for nothing y’know). If so, send it along to us at planet-science.news@nesta.org.uk with GIMME FIVE in the subject line.   Fancy seeing your name in print?  Your wish is our command.

This week’s stumper comes from Roy Badham who asks

What do you think scientists?

You will need:

• A selection of small geodes.
• Some 2 Molar hydrochloric acid.
• A beaker.
• A hammer and a mat or other surface to hammer on.
• Eye and hand protection.

What you do

Experiment 1

1. Take a geode and place it in the beaker, then put on your eye and hand protection.
2. Drop some of the hydrochloric acid on the geode and watch if it starts to bubble and froth.

Experiment 2

1. Take a fresh geode and place it on a mat.
2. While wearing your hand and eye protection, hit the geode with the hammer. Hit firmly to get it to crack but try not to smash it entirely. You may find it useful to stick the geode to the mat with Blu Tack, or hold it with tongs (not your fingers).
3. Once cracked, have a look at what you find inside.

What's going on?

Geodes form in both sedimentary rocks and in igneous rocks (rocks formed from cooled lava). Although these are very different ways for rocks to form, they both can produce rocks with holes in them, either from escaping gas or from water washing minerals away. Although this seems to be a plausible explanation for their formation it may not be the entire story. It is still unclear why this should lead to the spherical shells of rock which are easily removed from the bulk of the rock around them.

If the rock is porous, water can flow into the cavity, carrying dissolved minerals. These minerals are deposited on the inside of the cavity in the same way that limescale would build up on a sink.

Over a long period of time, over 200 million years, the minerals form crystals which can fill the entire cavity. If the minerals are deposited slowly, large crystals form on the inside. If the minerals are deposited more quickly - by water flowing more rapidly through the cavity - the crystals are small and there tends to be layers of different coloured deposits.

The colour of the crystals inside the cavity is determined by the mineral content of the water that flowed through it. Most often the water contains silicon dioxide which produces white quartz crystals, but other minerals can give the quartz colour, or produce entirely different crystals.

When concentrated hydrochloric acid is dropped onto the geode, if it is a sedimentary geode made of limestone, the limestone will react. Limestone is calcium carbonate and the reaction with hydrochloric acid produces calcium chloride, water and carbon dioxide. It is the carbon dioxide which produces the fizzing and bubbling.

Special safety advice

Eye and hand protection should be worn, along with long sleeves when cracking open the geodes. Don't be tempted to hold the geode with your fingers. Anyone observing should be far enough away to not be hit by splinters of rock. Wear appropriate protection with the hydrochloric acid and do not try to break open this geode and there may be residual acid on it.

This film clip can be viewed on Planet SciCast.

Keep checking back for new films and, whilst you’re about it - how about submitting one of your own?

This week we have TEN packs of three Flipsides to give away (Oct, Nov, Dec issues).  For more details about Flipsides check out their site.

“How can they do it?” you ask yourselves.  You don’t want to know. But suffice to say we at Planet Science can be pre-tty persuasive. Anyway what are we wasting time here for, email in quickly before you lose your chance!

If you’d like to win a pack then email us with your name and address, and the words ‘THREE FOR FREE’ in the subject line, to planet-science.news@nesta.org.uk.

This week we’re looking at the new website PEEP (Physics and Ethics Education Project). It has been built to match the new GCSE syllabi with their emphasis on How Science Works and ethical issues in science.  Students can find information on a wide range of ethical issues plus activities and challenges.  There’s also the option to have an online discussion which will give opportunities to practice argument. The site has been updated with the new A level specs (see Search by Syllabus).

The section on medical physics, for example, describes MRI amongst other medical techniques.  It queries when costly medical treatment might be too much and who decides what is a reasonable cost for medical treatment.

PEEP has a sister site, the original, focusing on Bioethics.