Growing Halite (Salt) Crystals


Purpose of Demonstration: To demonstrate the crystal growth of a common but extremely important household mineral that is rarely seen in its actual crystal form. Humans cannot live without halite (table salt). Yet this mineral is a combination of two elements, chlorine and sodium, with chlorine being a very toxic and deadly substance to humans. But combine the two to form halite or NaCl (sodium chloride) and we got ordinary table salt. The most pure form is derived from sea salt, with secondary sources being ancient sea beds that have dried up to leave huge salt domes, where much of our salt is obtained. What we will do here is create our own little "mini-ocean" with a plastic container and create our own salt crystals.....and form our own crystals of halite....table salt.

Equipment Required: Its quite easy, just get a canister of table salt such as the Mortons Salt shown at left, and a container able to sit still for a few weeks, and some water. That's all it takes. At left you see the salt container and the bowl of water with as much salt as we can get to dissolve in the water already suspended. This takes the place of the salt water oceans and creates our own "mini-ocean of salt water.

Suggested Grade Level: Elementary School and up to gemological teaching level.

Degree of Difficulty: Easy.

Cautions: None really....just don't disturb the bowl while the crystals are forming.

Here's how it works: Simply let the water stand still for a few weeks. The crystals will do all the work.

Here is what you should see :

During Week #2

After about two weeks you should start seeing numerous square halite crystals starting to grow in the bottom of the dish as shown above. The water will appear to clear up but there is still a lot of halite to crystallize from the salt water still in the bowl.

During Week 4

You should start seeing nicely formed cubic halite crystals of fairly good size (1cm) start to form as the sodium chloride continues to crystallize out of the salt water solution, and continues to make the crystals grow larger.

During Week 6

Crystallization is complete

Now you should have some well defined halite crystals of fairly good size. Some will be colourless and clear, as shown at the top right hand of the photograph at left. Others will be white. You can add some food colouring to give your halite crystals some added character.

Or...You can grind them up into powder and use them for table salt....or start all over again to make new crystals.


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