FDST would basically be a gaseous form of DUST. DUST would turn into it in low pressure or in high velocities. FDST would turn back into DUST in high pressure or when in contact with other elements.
I made a Lua script to demonstrate the element:
To run the code just download it, put it in your TPT folder and type dofile("fdst_element.lua") in the console.
(Btw I had a weird issue where the element would not transition in low pressure even when I had set the LowPressure and LowPressureTransition properly. I'm pretty sure it was set correctly because when I changed the LowPressure value to a positive one it transitioned immediately. Not sure what caused it so I just made the transition in the update function.)
For the record, the third point of How to suggest an element applies here, and to some extent the second point does as well.
REMOVED!
Yeah, I'll try to extend the element. This was actually a byproduct from another thing I was making. I might just make it into a proper Lua script and post it into the Lua subforum.