Potassium APEX Mineral

Potassium (K #19) (Neo-Latin Kalium) is the next collectible element on the periodic table for my APEX mineral collection. 

Potassium starts row 4 (Period  4) on the periodic table.  This is the row where our transition metals (electrons start filling the 3rd shell) appear for the first time.

Wikipedia Potassium
Potassium Minerals - Most Potassium minerals are ionic compounds (salts).

My Potassium APEX mineral will have to be a salt even though I am trying to avoid these.  Sylvite (KCl) with 52% Potassium is easily the best choice.

Potassium metal is not produced in any quantity.  It must be carefully stored to prevent the formation of a surface layer of potassium superoxide which is a pressure sensitive explosive.  It will detonate when scratched and start a fire that is difficult to extinguish.

A tea of burnt wood creates "potash" which is primarily Potassium salts.  Plants contain hardly any other soluble minerals.  While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts.

Potassium was not understood for most of its history to be a fundamentally different substance from sodium mineral salts

Fertilizers consume 95% of global potassium chemical production

Potassium is critical to life.  It serves a key mechanism in nerve transmission.