Don't know what it is but it sounds like clay. You already have clay. Do you have a link to the specific product?

Where do you live?
What kind of grass do you have?
How did you fertilize and when?
How high/low do you mow?
and how do you water?

This is a mineral that forms into clay, so why would someone want to add clay to the clay soil they have. What your soil needs is organic matter.

Here is a link that might be useful: Montmorillonite

it is vitrified, so yes, it is clay - but because it is fired it doesn't break down, it opens up the structure

Is it fired to the ceramic stage where it really won't break down? Or is it fired like they do in Mexico at a low temp? Eventually Mexican fired pots melt back into mud.