Gypsum, talc, and misc questions

[skyhook]

How to differentiate Gypsum, talc( sichuan Steatite) and magnesium chloride ? Food grade types and I think all are white powders. I've not observed these materials up close yet.

From articles, steatite is mainly talc, magnesium silicate. Does steatite contains calcium and other minerals in signifcant amounts ?

 

Is there any good adding talc to the soil ?

Some articles says talc is linked to some health problems. If the talc is used for farming, like adding to the soil, instead of for cosmetic use, is it safe ? or is there a possibility that some unknown impurities in talc may accumulate in the crops ?

 

Generally is there any difference between food grade gypsum and construction grade gypsum ,and plaster of paris ?