Same as bentonite really.... something like a teaspoon has the surface area as a football field, so its a MAJOR booster of CEC.... I get it locally when I dig a hole.... otherwise, its a clay I would buy... used often, its most cheaply obtained from a pottery supply store or a cosmetic supply....
Suppose I should try and expound on this a bit. I did quite a bit of research into the bentonite clays back in the late 90's as we used them in reefs.
http://www.eytonsearth.org/bentonite-montmorillonite.php
"Bentonite is a name given to a particular clay that was originally found in Fort Benton, Eastern Wyoming. The name was given by W.C. Knight in 1898."
"Geologists often describe bentonite as a clay mineral containing Montmorillonite, which poses a rather curious problem, as Montmorillonite is a name of a particular clay that was discovered in Montmorillon, France, named by Mauduyt in 1847."
""The name montmorillonite is used currently both as a group name for all clay minerals with an expanding lattice, except vermiculite, and also as specific mineral name."
Ok. So, Bentonite (as commonly used) "contains" montmorillonite but is not the same thing. Azomite is not a bentonite nor a montmorillonite. The key thing to remember though is that bentonite and montmorillonite are typically applied as "bulk" terms and NOT specific to each clay type. Azomite contains a large percent of the weight as silica. Many bentonites have a high percentage as sodium.
It's only the most purified // highest grade of montmorillonite that is primarily Calcium based. All of these will be listed as such, since it demands a premium in all markets.
The cheapest and most common form of "bentonite" is sodium bentonite. This is used from sealing of radioactive waste, to plasters, to lining ponds sealing them for water. Guess my fathers construction company used this often and ordered it by the ton.
-One less known property of Montmorillonite clays is that they have an overall net negative charge. This in part is why you see them used in bodily applications. (as well the mineral content of course) In soils they serve to attract Cations with a greater affinity than would an inert particle (e.g. no net charge). Cumulatively the surface area and charge contribute to the high CEC value associated with montmorillonites and to a lesser degree bentonites.
-Another little known aspect of montmorillonites is that they can actually alter the charge of an adsorbed cation. There is no other component (that I'm aware of besides electrolysis) that can do this.
So there are many varieties, compositions and grades of these bentonites. Be sure to look for the one that will suit best for the application. Back with reefs, we could not use Silica or Sodium based clays; so we had to stick with Ca based montmorillonites. The one that gave the most positive results with SPS corals; is probably the only I would choose today.
Personally I would look at clays that are approved for human consumption. At least that will eliminate the "wild claims" many mfgs package with low grade clays. The brand I prefer is Approved for human consumption, has been tested by several universities and has been approved and used by NASA to prevent bone loss in space. That should make finding it easy as there's only one.
Edit: just was spilling random useless info. Not intended to be specifically directed at you Sea.
