It is actually aragonite. The bottom layer is sand and the top layer is more rocky. Then there is the blue layer. I had a discussion about it awhile back with the whole story. One good thing about it is that it holds my pH pretty constant when I use the CO2. I would remove the blue rocks...but my girlfriend wont let me (it is *our* fish tank).
The whole tank has been a work in progress. My girlfriend and I started in November. We started out with the blue rocks and the middle rock thing and 4 plastic plants. We then added the cave to the left for one of our fish. Next we pulled out the blue rocks and added the sand and then put the blue rocks back down. Then we put in some moneywort and water sprite. It wasn't growing all that much. We upgraded from a 30W light to a 96W light (in the last 3 weeks I have been using both lights together). Then we added some sword plants. Next, the branch looking thing on the right was added with some java moss attached to it. Add a little time and a lot of fiddling and this is where I am at. I dont plan on doing too much more since I will be moving soon enough. I am moving to Washignton D.C. in August and I might have an intermediary move from College Station, TX to Houston, TX before that.
Gig 'em Ags