I did not know that Acacia got that large.
Thats called a slab wood cut. Tough to keep it from checking, warping, etc when it dries. I have been experimenting myself. Takes a year or so. The middle darker rings are called heart wood. I have cut apple that looked a lot like that in shape and color accept for the bark.
OK.. now I'm totallyguessing but... Acacia is a tropical wood so maybe it holds a lot of water? This might slow the drying process and help reduce checking.