Its a clay as best I understand...Is there spose to be a pic of a particular rock that we should be able to see? If its the clay you want I have access to it Its used in beauty facial stuff so I can get in bulk.. Ill check my catalogues and make sure im thinking of the right stuff..
It's chalk. Like in the cliffs of Dover. Montmorillonite is the clay which is a swelling clay. If you put montmorillonite into your tank, it would be a cloudy mess. It's used along with bentonite to aid in hole stability when drilling in oil and minerals. Probably more geology than you wanted to know, but I didn't want people to put montmorillonite into their tanks and kill all their shrimp.