Whereas phosphatic rocks are feedstock for both conventional and unconventional phosphate fertilizers, potassium silicates, such as feldspars, biotite, phlogopite, and muscovite, and rocks with feldspathoids, such as leucite, nepheline and clayrich sediments, especially illite, are the basis for alternative potassium fertilization (Straaten, 2010).
As K sources, the feldspathoids nepheline and balliranoite and biotite mica could be considered, with high weathering rates of the latter according to the Goldich dissolution series (Goldich, 1938).
The feldspathoids nepheline and balliranoite, zeolite analcime and feldspar sanidine, which include Na in their chemical composition, may be the minerals that release Na, making it available in solution.
A small amount of pseudomorphs after feldspathoid (sodalite?
Back-scattered electron and secondary electron images of altered feldspathoids confirmed zones with different ratios of intimately intergrown thomsonite and gonnardite resembling primary feldspathoid zoning and shaping.
The microphenocrysts of totally zeolitized feldspathoid are clouded, reminding primary sodalite crystals only in their sub-rounded morphology (see Plate I, 3).