Diadochite was first scientifically analyzed by August Breithaupt in 1837. His specimens were from the type locale, the alum quarries at Arnsbach near Schmiedefeld in Thüringen. The first description was made by Erdmann in 1831 in Belgium. The dripstone like mineral concretion is mostly porous and soft and grows much faster than dripstones of calcite. From the mineralogic view it is:
Diadochite has no crystal structure, it has no cleavage, is amorphous and gel-like. It has an enormous range of consistency and colour, which is a result of changing amounts of the components. Typical percentages of the main components are Fe ~30%, P2O5 ~30%, SO4 ~10%. Typical minor components are Al, As, Ca, Cu, K, Mo, U, V. In general aluminium compunds produce blue and green colours, phosphorus-iron compunds yellow and beige colours.
Diadochite is rather rare, but in old alum mines it is formed as secondary mineral in huge amounts. It is formed by oxidation of iron sulfide (markasite, pyrite) and phosphorite which produced sulfuric and phosphoric acid. Those strong acids are able to solute iron and other metals from the surrounding rock and dislocate them. This process is partly induced by micro organisms.