Nodule in Limestone

["Beverley Wright" <Bev.Wright@xxxxxxxxxxxxxx>]

Hi everybody,

My experience of the various limestones is limited, so
this is a first for me.

I picked up a piece (when I say I, I mean we (it weighs
in at a little over 13st)) of limestone from a local
reclamation yard. Was told it was Portland, but in
comparison to a piece of stone I know to be Portland, I
don't think so. There seem to be too many impurities in
it, some appear to be shells and there are the odd vein
of a pale off white substance running for three or four
inches, kind of like a paper tear, that is translucent
over a thin section and the oolitic structure is larger
than that in the Portland.

Anyway, the real find is a nodule. It is spherical in
shape about 3/4" across with a texture that reminds me
of a cauliflower. It is very hard, drew sparks from my
scutch chisel, and fell in two when I managed to prise
it out. I first thought it was iron because it appears
to be rusty on the outer edge with many sparkly silver
rods / filaments / rays / slivers emanating from the
centre in a veritable explosion. But it is not attracted
to a magnet.

Anyone have an idea as to what this nodule might be?

Not earth shattering in the great scheme of things, but
I'm intrigued.

Look forward to your thoughts.
Regards
Tony