hydroxyapatite is a mineral like your tooth, that's how it supports remineralization.

It's actually great stuff and works wonders for tooth sensitivity above and beyond fluoride shellac. I also order it from the more civilized world.

BioMin is available in the US and is similar, but I don't find it works better and I don't like that it doesn't have fluoride. (I live in an area without fluoride in the water)