Growing Salt Crystals.

Common salt, also known as sodium chloride or NaCl, have an interesting cystal structure. Water, Salt and lots of patience for one week, are the ingredients to grow salt crystals and get an easy science project. (6/3/2007) - Updated!


I saw a "Crystal growing" kit at the store one week ago, it shows nice and colorful crytals for science projects. I wonder; Why I should pay $10.00 USD just to see crystal growing? Using common salt and water, I can grow my own crystals. Not fancy crystals and colorful like the $10.00 one, but looks interesting anyway.


salt crystal


Salt (NaCl) crystal structure is highly ionically bonded. Large anions are arranged in cubic close packing and all the octahedral interstitial positions are filled with cations in this structure. This structure has an octahedral coordination (CN =6). This type of coordination predicted from the radius ratio calculation of cation to anion should be 0.732-0.414


In plain English, it means the salt crystal structure is a cube.


Upper photo: Salt crystals and molecule
Right photo: Salt molecules ionically bonded


growing salt crystal The recipe to grow salt crystal is simple:


1. On a cup, add some water.


2. Add salt and stir. Continue to add salt until the water is not able to dissolve it.


3. Put something to allow the salt to grow. A string hanging will be ok. A rock or stick may work also.


4. Place the cup on a place where it doesn't move.


After a few hours, two or three hours, you will see something growing on the string, just where the water reaches the string.


growing salt, one day Here is the "salt crystals" growing after one day.


after 2 days growing salt After 2 days.


after 4 days After 4 days.


after 7 days After 7 days.


after one week This is a chunk of salt growing on the string. It doesn't really looks like "salt crystals", it looks like "salt tree"


I'm kinda dissapointed because I don't see "crystals" hanging on the string, not even the "cube crystals" as I was expected.


But, WAIT! Look closer!


cube salt crystals Salt crystals are growing in the water!


For some reason, the cubic crystals are not growing on the string, the cubes are IN THE WATER!


It looks so cool, looks like ice cubes. Almost perfect crystal cubes. There is a crystal with a rectangle shaped.


Is very important not to disturb the cup for at least one week to see the crystal cubes. After several weeks, when the water evaporates completely, you will see salt cubes on the cup.


Again, the crystal doesn't looks fancy and big like the commercial ones, but you have it for free! Just from the kitchem items. Even if you use some food colorant, you can get colorful crystals.


I will experiment with more items from the kitchen. I'm sure epson salt have a diferent structure. Even baking soda should create "crystals"


Basically, earth crystals, grows in the same way, but it takes longer. After years and years, those crystals bonds and creates beautiful shapes. The shape depends of their molecular structure. The common one is Quartz.


Quartz is the second most common mineral in the Earth's continental crust. It is made up of a lattice of silica (SiO2) tetrahedra.


As soon I'm able to grow crystals with other materials, I will post an update.


June 2007 - UPDATE: Finally, I was able to harvest the crystals.


salt crystals on string Here are salt crystals growing at the string. Outside of the water only grows tiny crystals that looks white powder. Under the water grows the crystal cubes.


salt crystals Here are the salt crystals after the water completely evaporated. The tiny white crystals are formed because the water comes in contact with the humidity on the air, so we need to remove a chunk to be able to get the salt crystals with the cube shape.


Here is a chunk of crystals that I removed from the plastic cup. It takes 7 to 10 days to grow. I wonder if I can use some red food colorant and make some "ruby crystals"


I changed the "formula" and I tried to grow bigger crystals. This time, I used boiling water and I used a wider container with water only half inch high.


The crystals were growing faster, in 4 days big crystals started to grow but the water evaporated quickly and the cubes didn't grow as it should be, there is only "half cubes"


Here is a photo showing the size of the salt crystals that I was able to grow. Some crystals are 5mm wide. The right ones are the common salt crystals. Those grains are so tiny but are perfect cubes, so, no matter what is the size of the salt crystals, it will be always cubic shapes.


salt under the microscope You don't believe me?


Here is another photo showing the tiny salt crystals are cubes.



huge salt cube crystal Here is one of the crystal cubes that I was able to grow. I wonder if I can put this salt cube on a ring?


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