Fossil from North Norfolk coast, UK This palm-sized rock is from the beach at Eccles-on-Sea (North Sea coastline).

I can see four types of material:


A brown, slightly translucent, 6cm tubular fossil(?) that I can mark with a steel blade;
Coarse, light material--stained reddish-brown in places--that I can scratch away with a fingernail;
Hard, dimpled, dark-brown material that I can't scratch (iron perhaps?); and
Shiny black stone that I can't scratch.


I'm mostly interested in the fossil--if it is a fossil. Thank you. :-)
The round one is a belemnite... The grid-shaped fossil is a bryozoan. Bryozoans were (and are) marine colony building organisms often encrusting shells and other hardgrounds in the oceans. There are also solitary bryozoan colonies, which form screw-like shapes. 

A nice picture of a bryozoan similar to yours can be seen here