Rocks (especially agate)

I had a smashing day up London recently, which involved a visit to the national history museum.
(It also involved walking though Kensington Gardens, and along Oxford street and lots of sun and happy times.)
We went to the mineral section. I've always been a little disappointed in the mineral collection at the N.H.M, it was a nice way of displaying things but it always felt rather empty. Apparently this is because that wasn't really the mineral section, it was just a random extra bit with cool display windows.
The real mineral section is much bigger and much more informative. Now I am going to spend the rest of this post talking about rocks and other things in the red section.
Consider yourself duly warned.

Firstly, did you know that some minerals glow under UV light? Why this is necessary I don't know, because you don't tend to find much UV light in caves, but it does look pretty funky. Other things I found fairly interesting were the different forms of Chalcopyrite (I only know it because I visited a mine in Cornwall, but I didn't know it came in such a solid block.) Also it's not just trees that you can age by their bands, it's actually quite a lot of things. You can age shells and ram horns by them, and probably even more stuff than that.
There was also this rock, and you could count the bands to tell the calendar of the mine it was found it! How crazy is that! 

So I acquired a pretty neat piece of Botswana grey agate and you can really see the layers curving round from a central triangle,especially with the alternating translucent grey and opaque off-white.
I was interested to know why agate looked like this, and in case you did too, here's what Wikipedia has to say:
"In the formation of an ordinary agate, it is probable that waters containing silica in solution—derived, perhaps, from the decomposition of some of the silicates in the lava itself—percolated through the rock and deposited a siliceous coating on the interior of the vapour-vesicles. Variations in the character of the solution or in the conditions of deposition may cause a corresponding variation in the successive layers, so that bands of chalcedony often alternate with layers of crystalline quartz."  


Also I was interested to learn from the museum and Wikipedia that those coloured ring glass slice things are actually agate, and generic geodes are too! Although I think that generic geodes are dyed agate with clear quartz crystals inside.

Except the fossil. That's not agate.

This means that all of these are actually agate, just different varieties and forms. Isn't that exiting!







I would also like to say a very big thanks to my sister for drudging along with me. I'm sorry we didn't find more dinosaurs.