Crystals Can Grow    
        Growing Mono Ammonium Phosphate Crystals
          and Potassium Dihydrogen Phosphate Crystals

    Cochise College                                     

    Geology Home Page               

    Roger Weller, geology instructor 
    last edited:  12/22/15   
    copyright 2015-R.Weller


  mono ammonium phosphate crystals colored by yellow food dye 

  mono ammonium phosphate crystals colored blue by food dye


        Mono ammonium dihydrogen phosphate and potassium dihydrogen
   phosphate (KDP) are also excellent chemicals for growing crystals.  These
   chemicals are not available in drug stores or hardware stores and therefore must
   be ordered from chemical supply companies.  These chemicals work well by either
   supersaturation or saturation techniques.

        One of the commercial growing kits, The Smithsonian, uses mono ammonium
   phosphate in half of the experiments and potassium alum in the

        Mono ammonium phosphate produces crystals in the Tetragonal system of 
   crystal symmetry.  The most common crystal form is a four-sided, long column
   capped at each end by four-sided pyramids. 

    Because this crystal of mono ammonium phosphate grew in a cluster,
    the 4-sided pyramid did not form at the other end of the crystal.

   At different stages in its growth, this crystal of mono ammonium 
   phosphate developed imperfections.  Consequently the different stages
   in its growth can be observed.  This type of crystal in which stages can
   be observed is referred to as a "phantom crystal".

   In its pure form, mono ammonium phosphate is colorless and

   A crowded cluster of mono ammonium phosphate crystals

   A closer view of the cluster of mono ammonium phosphate crystals

        These colorless crystals are quite beautiful, but if you want to jazz up your
   specimen, you can put a large quantity of food coloring in your growing

     The following photos are of mono ammonium phosphate crystals that were
   grown by the evaporation method in an almost opaque solution containing
   a dark blue food coloring.


   The blue color almost makes these crystals look like copper sulfate,
   but the crystal shape identifies the material as mono ammonium


   Crystallization is a purification process.  Notice that the tips of the crystal are
   clear    and colorless and have been able to exclude the blue food coloring
   even though the growing solution was an extremely dark blue color.



  photomicrograph of trapped dye solution in mono ammonium phosphate
  crystal (used 10x power microscope)

  closer view of the above specimen (30x power)
  The crystal is clear, color comes from pockets of dye in solution.


   mono ammonium phosphate colored yellow by food dye


   closer view of the previous specimen

   web link for potassium dihydrogen phosphate  (KDP)
             VIDEO: Growing KDP Crystals