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601 Views 5 Replies Last post: Oct 24, 2013 7:35 AM by MikeHardman RSS
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Oct 20, 2013 11:57 PM

Silver metal looking rock found in durham

I found this silver coloured stone in my front garden in Durham it is 3cm round, weighs 19g and looks like this [although it doesn't look blue]

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    Oct 21, 2013 3:30 PM (in response to Claire)
    Re: Silver metal looking rock found in durham

    Claire,

     

    Very interesting.

    I've never seen that sort of texture before.

    The lump obviously has characteristics of being somewhat molten and apparently fallen - smoothish surface, globular overall, indentations of a couple of bars or some other object it landed on.

    But the surface texture - that sort of flaky-meshiness - defeats me. They add ingredients to steel mixes by tossing them into the top (not in all processes, just some). I wonder if this is a small wodge of nickel (eg.) flakes that was tossed in and got splashed out before it dissolved properly. Alternatively, it could be some of the molten metal in the crust at the top, where it was beginning to crystallize, getting splashed-out of the cauldron.

     

    I am presuming the interior is of similar composition to the exterior; that may be a false, granted.

     

    So, I'm fairly sure it is man-made, but I need some more information to progress from there...

     

    1. Density.

    You state it is '3cm round'. Do you mean 3cm in circumference?

    That will allow me to determine its density, approximately.

    But we could get a more accurate figure for density if you used the immersion method to determine its volume... There are various ways to do this, all of which introduce a small error. Here's one way: Find a container just big enough to hold the specimen, find another container a bit bigger and put the smaller container in it, fill the smaller container carefully to the brim with water (if any water spills into the larger container, carefully soak it up with kitchen towel), carefully lower the specimen into the water (this will displace water into the larger container), remove the smaller container, measure the volume of the water in the larger container (if you can find a measuring jug or other container small enough).

    The more-carefully and accurately you can do that, the better.

    Tell me that volume (preferably in cc or ml).

     

    2. Magnetism.

    Please test it with a magnet (the stronger the better).

    Let us know if there is any reaction.

    (It is unlikely, but also test to see if the object itself is magnetic: bring a steel object such as a knife or scissors close to it, and see if it is attracted.)

     

    3. Hardness.

    If you press into it with a sharp hard point (eg. that on a pair of compasses or dividers), do you leave an indentation?

    (You could also try hitting it with a hammer to see if it leaves a mark; hit softly to start with, in case it is quite soft.)

     

    4. Provenance.

    What do you know of the history of your 'front garden in Durham'?

    Was the soil imported from somewhere else or is it, as far as you know, the local soil?

     

    5. History.

    Was there even mining or smelting industry in the area (and we could be going back a couple of hundred years)?

     

    Mike

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        Oct 22, 2013 10:38 PM (in response to Claire)
        Re: Silver metal looking rock found in durham

        Claire,

         

        My hunch is that it is largely metal (rather than metallic ore).

        That is it is a metal or an alloy.

         

        From your measurements, I make the volume about 4ml,

        and since the mass is 19g,

        the density is about 4.75g/ml.

         

        There are not many metals around that density.

        The closest is titanium.

        ...Which just happens to be silvery-coloured, hard, non-magnetic, and resistive to oxidation/corrosion - just like your specimen...

        Alloys high in titanium will be of similar density.

         

        I can't be sure, but let's suppose it is titanium or titanium alloy.

         

        I can't think of a reason why titanium or titanium alloy would be associated with coal mining.

        Most of the world's titanium comes from mineral sand deposits, and there are no suitable ones in the UK.

        So I suspect it must have come from an industrial process that uses titanium, and does so in a way that involves molten metal. A metal foundry is the obvious candidate (titanium can be alloyed with many metals, and used on its own - see http://en.wikipedia.org/wiki/Titanium). I wonder if you have- or had one in your area...

         

        But what about that flaky-meshiness?...

        Some possibilities:

        1. Titanium can form crystallites (like you see on galvanized surfaces such as Armco at the side of a road or on corrugated iron sheets).

        2. In some circumstances, titanium exists as sinter - a particulate form useful as a raw material in some forming processes (many metals, not just titanium, can be sintered).

        3. For part of its processing life, titanium exists as what is called 'sponge'. You can see an example of that in the Wiki link above. If we were to see that close-up, we might well see what are called dendrites - the technical term for what I have referred-to as flaky-meshiness. Titanium sponge is used as a raw material in some processes, in which it is melted. (Dendrites are mentioned several times in this book on titanium - 'Titanium: Past, Present, and Future',  a Report of the Panel on Assessment of Titanium Availability: Current and Future Needs of the Committee on Technical Aspects of Critical and Strategic Materials, National Academies, 1983). Here is a photo of dendrites similar to yours, though probably in a different metal (from this paper on melting technologies).

         

        So, finally!...

        I suspect your specimen is a piece of titanium sponge that had partly-melted, but escaped from its process; perhaps it got splashed-out of the furnace. How it came to be in your garden, we may never know.

         

        That's the best I can do.

         

        Hope that helps!

         

        Mike

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