Hi Goldenprospector.
Do you have an angle grinder? Buy a diamond edged wheel (not overly dear and useful for other things as well) and cut a decent groove along the area you would like it to split. Make sure you are able to hold the rock immobile while doing that.
Then release it and locate a wedge or sacrificial chisel in the groove and give it a good whack.
Maybe even you may want to cut it all the way through but then a natural split maybe better. Your gamble.
Chances are it might split where you want rather than splinter into bits.
Only other suggestion make some friends in a rockhounds club with access to a slab saw.