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528 Views 5 Replies Last post: Jul 19, 2013 8:39 PM by MikeHardman RSS
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Jul 12, 2013 6:52 PM

Complete Beginner

My partner brought me a rocks and minerals book from the National History Museum on our most recent visit. I found this laying on the floor in a car park in Derbyshire for my  first ever ID to build a collection.  Looking at my nature guide I think it could be Ignimbrite?

 

I would also be very grateful for ANY advice in finding and cleaning samples,  The peak district is a stone’s throw away and should I invest in a geo hammer and chisel? 

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  • Currently Being Moderated
    Jul 12, 2013 10:57 PM (in response to shegeek101)
    Re: Complete Beginner

    Don't be put off, but I suspect it is man-made.

    I think it is probably clinker - a waste product of some industrial processes, like slag.

    Search this page for 'Blast-furnace slag clinker before grinding' and you'll see a lump somewhat like yours

    - http://www.nachi.org/constituent-materials-concrete.htm.

     

    However, your specimen contains no holes (vesicles), so there is a chance it is natural.

    But it is not ideal for ignimbrite. Ignimbrite is usually less multicoloured than yours. Also ideally, the clasts/shards within it should show some plastic deformation, reflecting their being like 'hot glass' when they were deposited from the glowing ash cloud (see here - http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/ignimbrite_welded_page.html).

    To confirm a rock as being ignimbrite, it should also be inspected under a petrological microscope - to understand the minerals, the matrix, and their textures. And it would be good to associate it with a suitable vocanic terrain.

     

    So - suitable characters might prove a rock to be an ignimbrite, but their absence does not rule it out.

     

    If your rock is not an ignimbrite, what is it?

    It may be an agglomerate or volcanic breccia or non-volcanic breccia, for instance.

     

    Without microscopic examination, what you'll get here are opinions.

    And somebody else may have a different opinion to me.

     

     

    Your other questions:

     

    - Finding specimens: Where to start?! Anywhere and everywhere. You may expect me to read-into your question that you are looking for 'good specimens'. Well, that doesn't really help me - because it all depends on what you are interested in. You can find good specimens in the facades of city banks, and on beaches - not just in rock ourcrops. In buildings and on the beach, you have the advantage of being able to see 'inside' the specimens - because they have been polished and/or wetted. You can also find specimens on eBay and such like, and in museums. Both of the latter may provide inadvertent help in your quest: they may indicate where they came from...

     

    - Cleaning specimens: this is basically curation. There are lots of techniques and technologies, such as ultra-sonic cleaning baths. A visit to a museum might be useful for you - so you might actually see curation in progress (make an appointment). Perhaps even better than a museum, see if you can wangle youself into a geology (or earth science) department at a university - and get somebody to show you. You should also develop/adopt a system for documenting your specimens. That may involve keeping a card with wach one, or numbering the specimens and keeping the info in a book.

     

    - Hammer and chisel: mmmm... There are many sites where such tools should not be used. That's because of degradation. Some sites are small and have been almost completely destroyed by collectors. As with many things, collecting should be done responsibly. I'd like to say more, but it is a big topic, and I could be writing for a long time! Again, if you can ask at a museum or geology dept., you might get the most useful guidance.

     

     

    Mike

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        Jul 13, 2013 1:24 PM (in response to shegeek101)
        Re: Complete Beginner

        Clinker it is, then.

         

        Your database sounds good. Well done. That would enable you in include photos and various web resources as well as numbers identifying the specimens.

         

        Definitely better to find rather than buy; that's part of the fun - quite right!

         

        Hammer and chisel have their place. For instance:

        - Collecting samples in hard rock terrain (massive granite/gneiss/quartzite/gabbro/etc.) You would often need a hammer it get a sample small enough to carry.

        - Collecting samples of/from loose material which may be in chunks that are too big (maybe in an old quarry, or on a beach). Be mindful of legal matters in such places - they may be SSSIs or otherwise protected.

        - More specific use, eg. splitting slates looking for reduction spots or pyrite; splitting nodules looking for ammonites.

        And apart from samples themselves, a hammer is often important for generating a fresh surface so you can study the minerals/fossils it contains with a hand lens. You'd do that in the field, for instance to avoid the need to collect a specimen (you can carry only so many!)

         

        A hand lens is something every geologist uses - get one of those. x10 magnification is enough for most purposes. But you can get fancier ones with sets of lenses enabling higher magnification if you want. A hand lens is an optical instrument, and as such there are technical issues to be aware of. A cheap lens will probably give a blurrier image than a more expensive one (the sharp area might be a very small part of the overall image). The image quality will also be degraded by dirt - so keep the cover in place when you are not using it, and clean the lens carefull (try not to grind dirt across the glass). A good lens will have coatings - again, be careful not to scratch. And a big lens (large diameter) will be easier to use - it will have a larger sharp area and it will give a brighter image.

        Here's a review of hand lenses

        - http://www.discoverwildlife.com/british-wildlife/test-hand-lenses.

         

        I use a hand lens for botany and entomolgy these days. But when I was more of a geologist, I used to keep it attached to my compass-clinometer (partly as a means of avoiding losing it!) That is something you might keep in mind for the future. It won't help much with finding and collecting the specimens that are your current focus. But it is essential when map-making (and map reading), and working on structural geology (involving the inclination of surfaces such as bedding planes).

        Here's how to use one - http://www.ukescc.co.uk/products/compass.html (nice job by Don Mackenzie and Helen Wilkins of Derby Uni.)

         

        I have a feeling we may be seeing you post a question or two on NaturePlus!

         

        Mike

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            Jul 19, 2013 8:39 PM (in response to shegeek101)
            Re: Complete Beginner

            Yes - chert is likely, partly since it doesn't have much of a crust.

             

            But read-up on chert and flint (refs below) and you'll see the distinction is rather slim.

            The key point to note is that flint is a type of chert. So if in doubt, you can initially say a particular specimen is chert, and later refine your view to say it is flint, assuming that to be the the outcome of your further research and deliberations.

             

            Refs:

            - Luanne's flint doc

            - NaturePlus chert doc

             

            You'll discover in your reading that chert/flint often includes or represents fossils. From your photo it seems there might be fossil fragments in your specimen.

             

             

            On a more general note: please start a new question for each specimen or group of specimens. Otherwise we run the risk of threads getting long and of them losing focus. The exception would be where you have other specimens related to the original one. For instance, maybe you had a tree ID question, but had to wait some months before you could take and post a photo of the seeds.

             

             

            Mike

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