The Game of Onyx

( Text and web page by Dariusz Stachowski. )
 

( A game in progress. )

The Game

Two players.  One player takes black, the other white.  Both take turns to place a piece of their colour on the board shown above and aim to form a connected chain of pieces that links opposite sides of the board.  The player with the black pieces aims for a vertical connection, the other player aims for a horizontal connection.  The nodes in the corners of the board are common to both adjoining edges.  Black ( vertical ) goes first.

Easy so far, but there are a few rules that give the game its particular flavour:

The Midpoint Rule.   A player may play at the midpoint of a 'square' only if none of the four corners of the square are occupied.  In the following diagram neither player may play on any of the nodes marked A to F.  The other midpoint square nodes are playable.

( Invalid midpoint moves. )

The Capture Rule.   Pieces can be 'captured' during the course of a game.  When a piece is captured it is removed from the board.  If the midpoint node of a 'square' is unoccupied a player can capture by completing a configuration in which all four corners of the square are occupied with both players occupying opposite corners of the square.  The other player's pieces are then removed from the square.  In the following diagram white can play on the node marked A to capture the two black pieces in the square.  White can play at B, but this does not capture since the midpoint node is occupied.

( Capture, before and after. )

Double Capture.   A double capture is allowed.  In the following diagram white captures four black pieces with one move at the node marked A.

( A double capture, before and after. )

The Swap Rule.   The second player ( white, horizontal ) has the option to 'swap' immediately after the first player has made his first move ( black, vertical. )  If swapped the roles will be reversed.  The first player will take the white pieces, will have to aim for a horizontal connection and will play against his own first move.  The second player is given a swap option in order to counter the first play advantage that the first player would otherwise have.

Variations

There are two variations.  A game can start either with an empty board or with each player having four starting pieces at the edges of the board.

( Initial layout with starting pieces. )

More Information

Play by eMail.   Onyx can be played by eMail at Richard Rognlie's PBeM server [ http://www.gamerz.net/pbmserv/ ].  The server controls the game and forwards eMails between you and your opponent.

Links.   An Abstract Games article about Onyx used to be at [ http://www.abstractgamesmagazine.com/onyx.html ].  An archive copy is available at [ Archive - Onyx ].  The article explains some of the history behind the game and also the logic of adopting the odd looking board and its rules.