Your not really helping the guy but doing more to confuse him.
Mark there is no reason why you should not use mahogany whatsoever.
It turns fine, holds a great finish and lasts as long as any other wood but if you want a fancy grain then go for other woods.
Any of the many variaties will make a pen and you can shape or engrave / pyro some character into them but you will look hard to find interesting grain pattern in them.
Neil will correct me but I think it is slow growing therefore tight grain.