Crystals Can Grow    
                         Growing Salt 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
 

   

    Naturally formed crystals of halite (salt).  The blue halite (sodium-rich)
    crystals formed first and were later overgrown by clear salt crystals.

 

        Growing nice crystals of common table salt is difficult for several reasons. 
   First of all, you cannot grow it by the supersaturated technique method because
   the solubility curve is almost flat.  In other words, by raising the temperature of
   the water, you really cannot dissolve additional salt above the normal saturated
   level.  In the super saturation technique the excess chemical that was dissolved
   at the higher temperature would come out of the solution as the temperature cools. 
   Alum works well with the supersaturated technique, table salt doesn't.
 

        Second, the only way to grow salt crystals is by evaporation.  Most commonly,
   hundreds of tiny crystals form instead of just a few isolated crystals that become
   seed crystals.  It has been suggested that one should use pure salt, not iodized
   salt because the iodine added to regular table salt favors the production of tiny
   crystals.   Sea salt or pickling salt should be used in trying to grow salt crystals.

   
 

    Pickling salt is just pure salt.

 

        It is also important not to disturb the salt solution once it has been into a
   growing container because the slightest ripple will cause small crystals to form. 
   Dust settling on the solution will also produce unwanted seed crystals.
 

   

        The lighter cluster of salt crystals are floating at the surface of the evaporating
   salt solution and tiny salt crystals have dropped to the bottom of the dark-colored
   pan.  The average size of these crystals is about 1 millimeter.


   

        This is a closer view of the tiny cubic salt crystals that have settled to the
   bottom of the pan.


   

        If you allow allow all of the water in the pan of saltwater to evaporate, this is
   what you get.

 

  
 

        The salt crystals are all crowded together, but you can still pick out reflections
   off square crystal faces.


  

        The last bit of salt water to evaporate produces a coating of even tinier salt
   crystals on the earlier formed crystals.


   

    Here is a closer view of the coatings.

 

        The best salt crystals that I have seen grown were done entirely by accident. 
   For a science fair project a student put a tray of saltwater under a hot lamp to
   demonstrate the evaporation process.  He developed cubic crystals that were
   larger than one quarter inch.  Perhaps starting with a dilute salt solution with no
   seeds in  it, followed by rapid evaporation under a hot lamp might do the trick.

        Another possibility for growing larger salt crystals might be to start with an
   almost saturated solution of saltwater and then place a large cleavage fragment of
   salt in the solution before small seed crystals start to form.

        Here are some halite (salt) crystals that formed naturally by evaporation of
   Searles Lake, San Bernardino County, California.
 
   

   These salt crystals are actually pink in color.

second experiment
 

Another experiment that you try with salt is to grow a "crystal garden".
Start with a saturated solution of salt.  In other words dissolve as much salt as you
can in a half glass of water.  Lightly stuff about 6 Kleenex tissues into the water until
the tissues reach the top of the glass.  Put the glass away for two or three weeks
and forget about it.  As the water slowly evaporates, crystal cluster will form above
the surface of the glass.



Looks almost like cauliflower.



The salt crystals were very tiny.



Almost cloud-like.