What is my rock????

[Swilcock1]

Does anybody have any ideas what my sons rock is please?

It is 20cm in length & 14cm width, it's very dense & heavy.

Many thanks Joanne

 

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[Eu_citzen]

Looks like flint to me.

 

[IAMZIM]

I was thinking chert, which is very much like flint!

 

[DDancer]

I feel you are both correct but I'll add chalcedony and druzy quarts to the mix. Its a mixed up stone. Both chert and flint can exist together, banded variations are common in some areas, however this one also has the precursors to chert and flint, the translucent chalcedony knodules and quartz crystals. The amount of iron in chert is what differences it from flints.

 

[Eu_citzen]

In another thread it was mentioned this rock was found in York, UK I think.

As for chert/flint/chalcedony - hairsplitting. I'd like to claim flint is indistinguishable from chert and chalcedony without microscope.
While the environment it was found in may provide clues, chert & flint are often found in sedimentary rocks, which are common in the York area I'd like to recall.

All that said, the lines of *exact* identification are fuzzy at best. It's likely a mixture of all the above, minus drusy quartz. I find that rather rare in those environments. (note the rounded shape looks concreation like - suggesting a sedimentary origin to me)