I think the brickettes are made from coal (not entirely sure). I'm also unsure whether they contain potassium which I think is what Sue is looking for for her soil.

I might be wrong on the science of this postassium/charcoal stuff (I was wrong once during a debate in 1975 ), but, in any case, I put our woodstove ash and charcoal from my daughter's marshmellow firepits into the garden and work them in first chance I get - even in winter. I read that ash losses it's ability to help the soil if it's rained on or thoroughly wetted before being worked into the soil. I don;t understand it, I just go by that.