Insight for fossil?

[KoenJ]

I agree. In the red 'circle' (I'm not the best in drawing on a phone) you can see the start of the phragmacone, see http://www.renmanart.com/images/belemn.jpg.

Belemnites were quite abundant during the jurassic and cretaceous period, so chances are this find has that age. But they are also found in older deposits.

If you want to take your hobby to a higher level, it might be interesting to check a geological map from the location you've been to.