Chrome Alum Crystal

Chrome alum or chromium alum is a safe salt that produces dark, purplish crystals. It can be mixed with Potassium Alum to create almost any purple color you want!

Key Takeaways

  • An alum is a type of chemical compound with the general formula XAl(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium
  • Alum crystals form octahedral shapes in their purest form
  • Mixed Chrome Alum crystals consist of potassium alum (KAl(SO4)2·12H2O) mixed with chrome alum (KCr(SO4)2·12H2O)

Prepare Chrome Alum Crystals

  • Regular Alum
  • Chrome Alum (Potassium Chromium Alum) 
  • Distilled water
  • Beakers

How to Grow Chrome Alum Crystals

  1. Start by preparing two saturated salt solutions – one for each alum salt. This is done by heating distilled water in a beaker to near boiling and dissolving a maximum amount of salt in it. After cooling to room temperature the solution can be filtered. 
  2. Mix both the colorless alum and the dark greenish chrome alum solution. The ratio is for you to experiment: using more chrome alum solution will yield a darker purple color. 
  3. For growing large single crystals, a seed crystal can be prepared and then placed in the solution for further growth.

Experiment Video