I'm at the point where I really try to avoid agonizing over what each clay is called. It's just too confusing and different people have different definitions. Then you have the issue of people blending different clay types.
Ultimately, in my opinion, the type of clay is not the determining factor in how well a pot brews tea. More important considerations are the quality of each clay, the firing temperature, the size and shape of the pot, and the thickness of the pots walls.
First of all, it's good to know the following: zi = purple, hong = red, lu = green, hei = black, and duan = yellow. Also, sha = sand and ni = clay. According to most people, the term "zisha" (while it literally means purple sand) is an umbrella term which gets applied universally to all types of Yixing clay, regardless of color.
My understanding is that there is a family of darker clays collectively known as "zini"- this would include pin zini, dia cao qing, qing shui ni, zi qie ni, etc. There are many who will also separate high quality, pure, sandy purple clay, and specifically call that "zisha." In other words, zisha can mean zini and every other Yixing clay, or it can refer to a very specific type of sandy purple Yixing clay. Confused yet?
As for hongni, this means red clay, and I've always considered it to be in a different family than zini. As far as subdivisions of hongni, some people say zhuni (an extremely fine particle red clay that fuses at lower temperatures than other clays, but shrinks more and is denser when fired) belongs in the hongni family. Otherwise, people may talk about hongni in terms of what mountain it was mined from, and each having their own merits and accolades, but it's
mostly all considered the same type of clay.
Chrl42 and others are definitely more knowledgeable about the topic than I. Here is a great post chrl42 wrote over on Teadrunk-
http://teadrunk.org/viewtopic.php?id=47
My best advice is to not get too hung up on it. There' good clay and bad clay, fantastic clay and mediocre clay, good pots and bad pots. You have to try a bunch, pay some tuition and get your feet wet before you really start to understand. Good luck on your quest.
. And also reading from other sites, since as you can imagine there is no info or tea masters when it comes to tea in argentina. But I am still a newbie, and I still need try several different pots a clays to have a deeper understanding I guess 
I have been drinking tea for 3 to 4 years, have only a few pots (mainly tuition pots).
