There are many different types of slate available on the market today. English & Welsh slate is so far beyond most peoples budgets that it is no longer a viable option for anybody but the extremely wealthy. Most slate now comes from Brazil, India & China. The quality of Brazilian slate is superior to Chinese & Indian slate.
Brazilian slate is much more dense than Chinese & Indian material, so when it is split the result is a flat, even surface and a richer colour. If you are thinking about slate tiles although the Chinese & Indian varieties are cheaper, it may well be worth paying that little bit extra for Brazilian slate.