Mangroves naturally grow in mud.
My opinion is that you could do just as well with dirt from your backyard, which, after a month or two picks up the bacteria from your tank. Miracle Mud is mostly silica sand. I have a pic on my home computer, but not here at work. Let me know if you want me to post it.
Of course they claim that it is LS from the ocean, but many believe they dig it for free from a slough (where the Mangroves grow) and make a killing by charging +$10/ lb.
Miracle Mud has benefits of offering Iron and other trace elements that are not found in Aragonite sand and I have seen a Miracle Mud refugium that ran a tank very well for years with an unusually high ORP. And yet like any other tank, when the sand is left unaltered for too long (old tank syndrome), it started to have nuisance algae problems. So I guess what I'm saying is that it's no miracle, it's just another way to do a good reef aquarium.
My 2 cents
Edited, here's the pic
Edited by Mark Peterson - June 13 2008 at 10:54am