Magnesite is often regarded as a nuisance stone. It shares this unfortunate position with Howlite, as they are both often dyed to create a fake Turquoise, which is either missold to consumers, or branded as Turqurenite in an attempt to confuse.
Magnesite itself is an unusual stone with some interesting formations – to tell the truth, it often reminds me of the heads of cauliflower. It is chalky white and not a particularly decorative stone until it is dyed.
It is rather useful to keep a piece around to quickly show people how Turquoise can be faked, though.