I found this:
Pure Caribbean Aragonite
Specializing in substrate material only, Petroglyph Marketing offers 100% pure Caribbean aragonite of the highest quality at a good price. They even offer co-op buying for taking advantage of their group rates for substantial savings.

on about.com. It takes you to PureAragonite.com, but doesn't tell you a whole lot. Seems like it is good quality, so it should be fine. Hope that helps...