I found this rock in a forest in Brittany in the late 60s or early 70s and, as a child, always thought it was a meteorite. Now I am wondering if it really is?! It weighs 534g and is not magnetic. Can anyone help to identify it for me?
We need to know the density.
You've given us the mass; please could you determine the volume.
Here's some guidance - http://www.youtube.com/watch?v=ovdE_-FCWpc
Also, its streak would be useful
And how hard is it?
Can you scratch it with a penknife? glass?
Or can you manage to scratch those materials with the object?
I'm trying to get an idea of its Mohs hardness. Have a look here for more details
Given denisty, streak and hardness, as well as your photos, I ought to be able to give you a fairly short list of possibilities for what it is composed of.
Secondarily, we can consider if it might be a meteorite.
Well it has been fun and interesting doing the tests but I seem to have proved my childhood meteorite theory wrong, sadly!
Firstly, the density is 4.11 gm/ml (543g mass / 130ml volume).
A photo of the streak test is attached (where it all went wrong!)
Finally, I tried to scratch it with a penknife but couldn't. Because it is so rounded it hasn't got any sharp enough edges to try to scratch another object.
Thanks for all your help - it has been very educational. I would still like to know your thoughts on its possible identity.
Well, it is still an interesting object, even if not a meteorite!
I wonder about your density determination. If it was not for that, I would suggest haematite (hematite) (5.3).
There are minerals that fit colour, streak and hardness (over 5.5), and are fairly close in density:
- galaxite (desnity 4.23)
But it is too rare...
- maghemite (density 4.9)
But it is magnetic, so that does not match yours
So I suspect it is haematite (which can take various forms), and either you made a mistake in your density calculations and/or it may be impure and/or in may contain cavities.
Note that haematite is said to be "magnetic after heating"
I've never tried heating a piece of (non-magnetic) haematite to see if it really does become magnetic...
Hope that helps.
I agree (near enough) with your calculations (I get 532g/125ml = 4.26g/ml).
So galaxite has to be a possibility, on the grounds we have explored so far. But I have trouble believing it!
It would really need chemical testing and analysis under a microscope (looking for crystal textures and optical properties), which we can't do through the medium of this forum, and which would start to be expensive if taken to a lab.
So unfortunately, I can't give you an ID that I am confident of, sorry.
If you have a university with a geology department nearby, you could show up there looking desperate for help, and you might be lucky, ornot.
It looks very much like goethite to me. It has brown streak, according to mindat its density is 4.27 - 4.29 g/cm3 and it often has the botryoidal surface structure like this (eg. http://www.mindat.org/photo-605991.html). The hardness should be 5-5.5 which is approximatelly as hard as a good knife.