Quote: "@josephjk"0.75 gram, 15 mm approx.
This coin was identified for me on an another forum... does it exist in Numista? thanks

Yes, it is.
https://en.numista.com/catalogue/pieces101008.html
I agree that coin is Blanca. Felipe II. Cuenca. Calicó 815. But the mintmark isn't X.
It has patriarchal cross left and chalice under star right in obverse, patriarchal cross left and C right in reverse. No X.
The patriarchal cross is the symbol of the official of the mint Pedro Román, who worked in Cuenca in 1550-1576. The chalice under star and the letter C are mintmarks of Cuenca.
This design began in 1566, then this coin is between 1566 and 1576.