Skip navigation
615 Views 7 Replies Last post: Jul 21, 2014 1:40 PM by MikeHardman RSS
Currently Being Moderated

Jun 17, 2014 11:56 AM

Rock or Meteorite?

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?

Attachments:
  • Currently Being Moderated
    Jun 17, 2014 1:10 PM (in response to Elaine)
    Re: Rock or Meteorite?

    Elaine,

     

    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

    - http://meteorites.wustl.edu/id/streak.htm

     

    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

    - http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness

     

    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.

     

    Mike

    • Report Abuse
      • Currently Being Moderated
        Jul 2, 2014 7:40 AM (in response to Elaine)
        Re: Rock or Meteorite?

        Elaine,

         

        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)

          http://webmineral.com/data/Galaxite.shtml#.U7OjjJRyzpw

          But it is too rare... 

        - maghemite (density 4.9)

           http://webmineral.com/data/Maghemite.shtml#.U7Oj-pRyzpw

          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"

        - http://webmineral.com/data/Hematite.shtml#.U7Oo5ZRyzpw

        I've never tried heating a piece of (non-magnetic) haematite to see if it really does become magnetic...

         

        Hope that helps.

         

        Mike

        • Report Abuse
          • Currently Being Moderated
            Jul 18, 2014 4:02 PM (in response to Elaine)
            Re: Rock or Meteorite?

            Elaine,

             

            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.

             

            Mike

            • Report Abuse
  • Currently Being Moderated
    Jul 21, 2014 11:20 AM (in response to Elaine)
    Re: Rock or Meteorite?

    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.

    • Report Abuse
    • Currently Being Moderated
      Jul 21, 2014 1:40 PM (in response to Stativ)
      Re: Rock or Meteorite?

      Stativ,

       

      Welcome to NaturePlus.

       

      And thank you very much  - I am sure you are correct in that ID.

      I cannot explain how I overlooked goethite (though I was close with haematite).

       

      Mike

      • Report Abuse

More Like This

  • Retrieving data ...

Bookmarked by (0)

What the symbols mean

  • "correct" answer available
  • "helpful" answer