I found this rock while out walking it’s of a metallic Luster and black in colour, smooth to the feel but bumpy in places, with one small rough patch shown on the picture and no colour change anywhere. It is unusually heavy for its size it was found in a filed in bottisham in the middle of a recently ploughed field so was kinda lying on top in the mud. I have tested it’s hardness against a steel knife and it does not scratch but don’t have anything harder to test on it. I hope that there is enough information to start and please let me know if anything else is required

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  • $\begingroup$ Welcome to the site. Please, if posible, add some more info from this guide. eg you can do the displacement test and weigth the piece to have an aproximate density to clarify a bit what is composed about. earthscience.meta.stackexchange.com/questions/124/… $\endgroup$ – user12525 Feb 19 '19 at 16:53
  • $\begingroup$ For the volume you can do Science in this way: earthscience.meta.stackexchange.com/questions/1663/… $\endgroup$ – user12525 Feb 19 '19 at 16:54
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    $\begingroup$ I can’t get hold of accurate scales till tomorrow but a rough weight is 39g and it displaced about 8ml of water so density is 4.87 this is rough will get a more accurate reading tomorrow if this helps for now $\endgroup$ – Marco Fasulo Feb 19 '19 at 18:11
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    $\begingroup$ This is a repost of your previous question, which you should have edited to improve instead of posting another question. $\endgroup$ – Spencer Feb 20 '19 at 1:05
  • $\begingroup$ density will be important sw will whether it is magnetic or not. A face on look at the broken portion will help as well. $\endgroup$ – John Mar 30 '19 at 5:01

It appears your rock maybe a dark oxide coated large pebble. This type of coating is commonly composed of iron and or manganese oxides are is common known as desert varnish. Named after the fact that this type of coated rocks are common in desert environments.

Personally, I've seen these types of rocks in other areas besides deserts, like the Great plains of the Midwestern United States, that experience periodically arid conditions. In my opinion, microbiological activity may play a significant role it the formation of desert varnish.

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    $\begingroup$ Not sure about desert varnish in a recently ploughed field in Cambridge $\endgroup$ – Gimelist Feb 21 '19 at 10:01
  • $\begingroup$ @Gimelist stranger things have been "known to happen" youtu.be/liIlW-ovx0Y?t=54 $\endgroup$ – uhoh Mar 26 '19 at 0:45

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