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 If you have any geological question you'd like us to put to an expert then send it to us and we'll publish the answer here.
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Sara wrote in to ask:
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"What makes 'glow stones' glow?.
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Rockwatch Science Editor, Susanna Van Rose replies:
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Dear Sara,
You were luckier than me - I couldn't make my two glow stones glow. But I think this may be because where I live there's a lot of light from street lights and security lights, and I just couldn't get a dark enough place to see the effect. Or perhaps I didn't rub hard enough. I have seen this glow effect when quartz is being polished by a stone polisher (lapidary) using electrically-driven carborundum grinding wheels, and I imagine what you have seen is similar. He (he lapidary) called it the fire in the stone.
This glow or fire effect comes from quartz having the physical property of piezoelectricity. This long word means that some kinds of crystals, when they are stressed by mechanical means, such as rubbing or squeezing, respond by giving out electrical energy as a spark. You might have seen this in action in appliances in your own kitchen. If your home has a gas hob with automatic lighting, the clicking sound is pressure (squeezing) being applied to a piezoelectric substance, which makes it give out a spark which lights the gas.
You might also have seen the device sold in some chemists shops which stops mosquito bites from itching - called a zanza-click. I haven't yet found out why it makes the bites stop itching, but what it does is to blast the bite with piezoelectricity. I looked into my zanza-click, and I can see the spark when it clicks, so inside there too is a piezoelectric substance. Quartz and tourmaline are two of the best known natural crystals to produce piezoelectric effects. Whilst piezoelectricity is very useful commercially, it can be a nuisance to gemstone cutters working to polish either of these two kinds of crystal. It means they have to work slowly and carefully to avoid producing too much of what they call fire (glow), as this would make the stone hot and could cause it to crack as it heats and then cools down.
I tried 'piezoelectricity' for an internet search and it came up with quite a lot of history, and also quite a lot about commercial uses of the effect. You might like to do a search yourself
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Susanna van Rose
Rockwatch Science Editor
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Ellie wrote in to ask:
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"If the minerals in the human body are the same or different from minerals found in the Earth.
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Rockwatch Science Editor, Susanna Van Rose replies:
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Dear Ellie,
Apatite is one of the important minerals in the human body. This is the mineral that makes bones strong. To look at, apatite crystals from the mineral deposits in the Earth may be bluish and clear in which case they could be cut and used as gems. Other crystals of apatite may be duller colours, and have lots of inclusions or cracks in - then they're not suitable for gemstones. In bones, apatite crystals are fibrous, and wouldn't be suitable for gems. In bone, apatite crystals align themselves in the direction that gives the bones most strength. Many minerals are stronger, or harder in different directions through the crystals. They're continuously growing and replacing the bone that's already there, and this is how young people grow bigger, and how broken bones heal themselves.
Many years ago I broke my leg. It was mended by a surgeon putting in a metal strap which he screwed into the broken ends of my bones. (This wasn't painful- he put me under anaesthetic!). Over the next year, the stainless steel strap held my bone together while the apatite crystals re-grew to heal the break. Eventually I had another anaesthetic and the metal was all taken away. Whilst the metal was there doing the work of holding my bone together, the apatite crystals just grew any old way, and hadn't got themselves lined up for strength. So I then had to be a bit careful for another year, while the apatite crystals re-aligned themselves to give my bone its strength again. Now my leg's as good as new, and I can ski and do all the things I used to do, and this is just because the apatite crystals re-grew and now hold my leg together.
So, really, in answer to the question, minerals in the body are chemically the same, and have the same physical properties, but they look different from minerals that are found in the Earth.
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Susanna van Rose
Rockwatch Science Editor
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Matthew from Wales has written to Rockwatch with a letter for our experts. He wrote:
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"I 'lurve' Rockwatch magazines! And science! But I still have
five impossible-to-answer questions:
1. Can you prove the big bang?
2. What created the big bang?
3. How did this explosion cause life?
4. Can you prove the age of the Earth and dinosaurs?
5. Can you prove evolution?
Thanks - Matthew"
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Rockwatch Science Editor, Susanna Van Rose replies:
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Dear Matthew,
Thank you for your letter, and I'm so pleased to hear how much
you enjoy Rockwatch.
Your five unanswerable questions are very big questions and
you're right to call them unanswerable. I can't attempt to answer
most.
Your question number 4, about proving the age of the Earth and of
dinosaurs. Rockwatch magazine published an article about dating
the Earth, in issue 28. Maybe this was before you joined the club
- if so, contact Geraldine, and she'll see if she can find you a
copy. In issue 28, Cherry Lewis wrote about how rocks are given
ages in figures (rather than just saying one is older than the
other on the basis that it's underneath in the pile of layers).
Actually, Cherry has written a book about Arthur Holmes, the man
who discovered how to use radioactivity to date rocks. It's
called The Dating Game, and is published by Cambridge University
Press. You might like to read this - perhaps your local public
library has a copy. It's a history of his life, and explains why
he wanted to know, and how he came to find out, and all the
difficulties he came up against along the way.
Geologists find this radiometric method of dating rocks really
works. It's now been used on many rocks all over the world. It's
made it possible for example to work out the structure of groups
of folded rocks that contain no visible fossils. Also,
radiometric dating tells us numbers of millions of years for
fossil-bearing rocks; this is how we know for example that it was
65 million years ago that dinosaurs died out, from radiometric
dating of the rock layers that contain the last dinosaurs.
You tell me you're a fan of the National Museum of Wales, because
they have all these wonderful dinosaurs, fossils and minerals,
some of which are so huge. Geraldine and I will put the museum on
Rockwatch's list of places where we'd like to have an event next
winter, and hope that the planning all works out.
Will you be entering the Rockstar Competition this year? It
sounds as though you could write about the museum.... or probably
lots of other topics. There are 12 prizes this year, and you
never know, you might be one of this year's winners.
Best wishes,
Susanna van Rose
Rockwatch Science Editor
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Matthew also asked us to do an event in the Welsh National Museum in Cardiff which he says has plenty of dinosaur skeletons, loads of fossils and 'uncountable' minerals!
Matthew - The good news is that the Geologists' Association with Rockwatch will be taking place in Cardiff in November next year so I hope you will come along to that.
Thanks for writing in -
Geraldine
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