Thank you all gentlemen, for your input.
I had already been in that link website during my browsing, Wayne.
It appears to me that this is not likely to be a mill ball.
Those spheres are usuallly hardened steel, whereas my example is iron.
I have phoned a cement maker technician; the wearing of mill balls has a smooth texture.
Also i think that a mill ball, worn by continuous random tumbling, would get a alietory shape due to its variable movimentation and not such a regular one, which looks to have been submited to a specific rotation, orientated in a linear direction.
I know nothing about metalurgy either, but probably a steel mill ball woud not degradate through time in the same manner, with such corrugated and scaled look.
A remote probability would be considering that this ball was used for "hot shot", having been "stretched" in its itinerary through the barrel or, not hitting a direct impact target, having rolled on the ground in a regular manner (drum like), before cooling down.
Thing is i don't even know if hotshot was used in Portugal
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