Ammonium Alum

Formula: NH4Al(SO4)2·12H2O Ammonium Alum

The biggest specimen in my collection. Mass is 45g, growth time is 4 months.


  • Crystal system: isometric (cubic)
  • Crystal shape: octahedron
  • Color: transparent
  • Stability on air: stable


I prepared the compound by mixing hot concentrated solutions of aluminum sulfate and ammonium nitrate and then cooling the solution:

2Al2(SO4)3 + 3NH4NO3 → 3NH4Al(SO4)2·12H2O(s) + Al(NO3)3(aq)

Alum is much less soluble than aluminum nitrate and crystallizes, leaving Al(NO3)3 in the solution.

More direct way would be using ammonium sulfate (NH4)2SO4 instead of nitrate, but I had no supply of it at the moment.


One of the easiest compounds for growing. Solubility is relatively low (15g/100ml at room temperature), but increases significantly with heating. This makes this compound suitable for quick growing using cooling method.

However, I prefer to use slow evaporation method, as it produces clearer crystals.


The compound is safe.

More photos

Ammonium Alum

Ammonium Alum

Ammonium Alum

Ammonium Alum

Ammonium Alum