Geology

My friend Russell is a retired Professor of Geology.

Whenever I find something of interest (to me anyway) I send him a photo and ask for a full explanation. This erudite description comes from him.

Firstly the one on the right

" Definitely an arrow head, probably Early Stone Age or
manufactured by a poor Middle/Late Stone Age apprentice. Some of the
more sophisticated stone tools are flint (very fine-grained nature of
flint allows for a degree of finesse). Flat on one side is the norm -
thats where it may have nestled in the grubby palm of the maker."

And that on the left


"Looks like the "ballast" secreted by certain of the cephalopoda - the
purpose being to give them weight and momentum when they fire off
their water jets. Known as the "guard" and typical of Belemnites is
part of the inside of these small octopus-like creatures."


When I expressed my thoughts that it must just be a flint nodule...

"As regards the flint nodule - well of course it could be flint (or
silica gel) REPLACING a belemnite guard. A possible scenario: calcitic
belemnite guard is buried in chalky marine sediment (mostly the
remains of coccoliths). Later the calcite is dissolved, leaving a
guard-shaped hollow which is then filled by silica gel which turns
into a belemnite-guard-shaped flint nodule"

There you have it.