Hi rab7ies - if the green stuff is not organic, then it may be the mineral glauconite. Copper minerals do occur very very rarely in chalk and flint, so malachite is a possibility but unlikely.
I love your flint echinoids, they are uncommon on the Yorkshire coast unfortunately.
those are excellent Richard..will try to take a pic but its very fragile.
Although it is difficult to identify Gauthieria species and small Phymosoma species from flint casts, the balance of probability would be with Gauthieria radiata.
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