Balbo's Chess

Chess variant

Chess variant played on a diamond-shaped board with 70 squares.

Otherwise the rules of chess apply, with the following differences:

Pawn promotion in Balbo's Chess

On the three central files, the usual rules apply: one can select queen, rook, bishop or knight.
On the next two files (where the rooks start), the same rules apply (queen, rook, bishop or knight).
On the next two files (where the wing pawns start), one can only select a minor piece, i.e. a bishop or a knight.
On the other four files (where the pawns can only move to by capturing) the pawns do not promote, staying there as pawns. There they are useless unless they can capture again.

M. G. Balbo, 1974^[ChV.com]