you need to be more specific. I'm not sure what you're asking.
Are you wanting to find something else to be the clay component in a Mineralized Soil setup prep? In this case, a non-hardened clay, such as potters red clay, is recommended, since it provides the tiny particles with a high CEC (Cation-Exchange-Capacity) to improve the substrate-root contact, as well as imparting iron directly to the plant roots.
Are you looking for a supplement of sorts, like the old "Duplarit" Clay Balls, which could be put underneath an iron-demanding, heavy root feeder like Amazon Sword Plants? In this instance, the same potters red clay could be rolled up into marble sized balls, allowed to air dry, and placed beneath the root mass of heavy feeders, for a low-cost "Duplarit" subsitute.
The color of the clay is often determined by the mineral content. Red clays are higher in iron.
Are you looking to set up a "Quackenbush" style tank? These are often called a "kitty-litter substrate" tank, where a layer of dried clay, usually plain mined clay sold as kitty litter (no fragrances, clumping agents, etc), is supplemented with a slow-release fertilizer as an under layer, and is then capped with fine sand to keep the nutrients out of the water column. These can be remarkably successful with root feeding plants like Echinodorus and some of the more robust crypts. Fine leafed water sprite will become a jungle in these setups, but stem plants will NOT like this substrate for the long term. The soft clay will eventually slump, losing the individual particles, and the inter-particle spaces, and if not thoroughly inundated with roots (i.e., lots of sword plants) it can and will go anoxic.
Are you asking the difference between raw clay, such as pottery clay, and altered clay, like Soilmaster Select, which is a high-fired clay product. Firing the clay the way the SMS is, creates harder particles, with extremely high CEC ratios, but lower density.
I hope I may have hit on some of what you're asking.
Hope this helps,