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

   Virtual Geology Museum
   Hall of Minerals     
    Geology Home Page               

    Roger Weller, geology instructor  (wellerr@cochise.edu )
    last edited:  10/6/10   copyright 2010-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
   remainder.

        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
   transparent. 
 

  

   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
   solution.
 

     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 phosphate.


  


  

        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


 

closer view of the above specimen
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