Belgian bluestone has a blue-gray color and is relatively rich in small fossils in the stone. Over time, Belgian bluestone can show small black spots that do not affect the quality of the stone.
Chinese bluestone, on the other hand, is about 150 million years older than Belgian bluestone. This bluestone is rich in dolomite and is usually recognizable because small spheres of lime and white veins with spots have been incorporated in the rock. Dolomite present in Chinese bluestone can cause a slight browning over time. Incidentally, this discoloration does not have any negative effect on the quality of this bluestone.
The choice between Belgian and Chinese bluestone of a comparable quality will therefore mainly be determined by your personal taste.