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 (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

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

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.





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!

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.




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 another photo showing the tiny salt crystals are cubes.

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