Natural gypsum is the most economical way to supply calcium and sulfur for soil that is hard to cultivate. It works by separating clay particles through a natural chemical reaction without changing the pH of the soil.
Qld Organics Natural Gypsum:
is an all-natural product, sourced in Australia
has a controlled moisture content of 2-3%
is screened to less than 3mm & will flow freely through spreaders
is non-radioactive, with less than 1ppm cadmium
Benefits 
slow release of nutrients that feed plants over many months
increased earthworm activity
improved water retention and aeration
increased micro-organisms and beneficial bacteria
no burnt or damaged plants
pH neutral