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OK ---- I finally have had a minute to get my thoughts together. This type of concretion is formed because of the iron in it. They are common in Monument Valley here in the US. They are also found in the Northwest of Australia. They are also found on Mars. These concretions form in a sandstone layer where iron rich water is stored. By this, I mean the water does not move much; it is in a rather static state. Usually, the sandstone layer is close to the surface where evaporation can occur. As water enters it brings in more dissolved iron the concentration increases. Then there is a trigger - usually a hydrocarbons in the fluid system - that causes the iron to begin oxidizing, forming hematite. In the picture Neil posted, hematite is the shiny black-gray material. To get a more coherent explanation see this link - http://en.wikipedia.org/wiki/Navajo_Sandstone#Iron_oxide_concretions_.28Moqui_marbles.29In extreme condition, shinny hematite spheres can form. See this page - http://en.wikipedia.org/wiki/Hematite - CLICK ON THE PICTURE on the right. It will give you a larger picture where you will see spheres of hematite. These form in sandstones, lake and ocean bottoms as well as being deposited by super hot water. Neil, are you happy now? Lastly - WELCOME TO THE FORUM, BAILEY!
im sure its not(processed/refined) metal of any type.. it weighs 250g..about half of a 'bald' tennis ball in size if thats any help?
here is the piccy of the rock I have just received. I am posting it for bailey and here is his description ! hi...here's the rock,on the other side its perfectly round and smooth,its has an outer crust about 6 or 7mm deep,the inner crust is also spherical.i hope this isnt too big to send,i dont know much about cropping etc,but i can send better pics if you want.id be really interested to find out what this rock is and how it was formed....[attachment=10697]
Jim - why do these things form spherically?