Thought about it once when I ran out of titanium dioxide, I was even considering grinding up chalk then too.
Didn't end up doing it, decided if I make soap I want to be able to use it.
I haven't used talc in soap but I did use it in making my own solid antiperspirant stick. However, I am not using it since most of the information I found online about talc suggests it's not very good for you. There are articles on talc saying it is a carcinogenic. I don't know if it can pentrate skin from using talc soap but I suppose if you use it in a body powder then it will most certainly enter your body through your lungs.
I know the info should be taken with a pinch of salt but still ... The best thing would be to do some research before using it in your soap and then you can make an informed decision I made my deodorant stick with talc because I read it as one of the ingredients in commercial deodorants and I thought it was safe to use ...but after I read more about it I decided not to use it ... lesson learned.
I did try some corn starch in my soap though and it gave it a very creamy and smooth texture and it helped fix the scents beter.
Just my opinion
mari