Skip navigation
330 Views 2 Replies Last post: Aug 21, 2013 5:12 PM by Tammy RSS
Currently Being Moderated

Aug 13, 2013 12:10 PM

Identify rock from seashore

Had this rock for a year or so and cannot recall exactly where found.  It was on an English sea-shore and strongly thought to be north within a mile of Scalby Ness,

north of Scarborough, North Yorkshire.  The other location may be Dorset coast Charmouth area.  The rock appears to be in layers and has gold colour glints which hardly show in photos.  Measures about  9x6x4cm.  It's mass is 4.18 gms per 1ml.  Colour is more a dull browny than photos show.

Am really curious what it is.  Could you please identify ?       Tammy.

  • Currently Being Moderated
    Aug 13, 2013 1:22 PM (in response to Tammy)
    Re: Identify rock from seashore

    Tammy,

     

    Thanks for determining its density; that saves me asking and explaining.

    It is too light for iron, and even a bit light for haematite.

     

    I think it is a chunk of iron ore containing a lot of iron pyrites - going on the (density ~4.9g/ml), the numerous cubic crystal faces and glints of 'gold'. It seems unusual that it is as dull and 'rusty' as it is, but that could reflect the environment it was in (in situ or in storage) and/or particular original chemistry. This appearance is more common with marcasite (due to differing arrangement of the sulphide ions around the iron ions); both are iron sulphide (FeS2). But I'm fairly sure it is not marcasite, because of the cubic crystal structure (marcasite is orthorhombic).

    Unless...

    Well, you see, minerals can lie!

    There's a thing called pseudomorphy. That's where crystal(s) might look like a particular mineral going on the crystal shape/habit, but turn out to have been chemically altered to something else while retaining the shape/habit.

    ...And that is known to happen with pyrite-marcasite. For example, H. N. Stokes mentioned it in The Chemical News, 11jul1902 (vol.85), p.33 'On pyrite and marcasite'

    - http://booksnow2.scholarsportal.info/ebooks/oca1/19/chemicalnewsjo8586londuoft/chemicalnewsjo8586londuoft.pdf

    (slow to download because it is big (65Mb))

     

    The habit of the specimen as a whole seems unusual. I'm not sure what to make of that. It may have originated in a vein. I don't think it is of industrial origin. Thanks for the possible localities; in this case they don't help me much.

     

    In summary, I'm fairly sure it is iron ore, probably mainly iron sulphide, possibly marcasite replacing pyrite pseudomorphically.

     

    Mike

    • Report Abuse

More Like This

  • Retrieving data ...

Bookmarked by (0)

What the symbols mean

  • "correct" answer available
  • "helpful" answer