For this week's experiment, we are going to investigate a very important substance which most of us take for granted. Salt. While we hardly think about it as we sprinkle it on our food, in the past, salt was a very important and valuable substance. In addition to enhancing flavor, it is a vital substance in our diet. Before refrigeration, it was a very important way of preserving food.

We are going to take a close look at salt. You will need:

- table salt
- course or rock salt
- a magnifying glass
- a sheet of newspaper
- a hammer

Lets start by taking a close look at some table salt. Sprinkle a few grains of salt into your hand and look at it closely. If you have a magnifying glass, you can use that to get an even closer look. Even without the magnifying glass, you should be able to see that each of the grains is a tiny cube. With the magnifying glass or a microscope, even the tiny bits of salt around the grains are cubes. Why are all of the pieces cubes?

Take a large grain of salt from the rock salt. This salt is commonly used in making home-made ice cream (yum!) and in melting the ice on sidewalks. Get the largest piece you can find and then use a hammer to gently break it. You don't want to smash it into tiny bits. Instead, try to break it into 3 or 4 fairly large pieces. Notice the shape of the pieces. They also tend to be cubes.

Why does the salt break this way? Salt, like many other minerals, has a property known as cleavage. This means that the mineral contains weaknesses which cause it to break easier in one direction than in another. Some minerals, such as mica, only have cleavage in one direction. They tend to break into thin, flat sheets. Salt, which is also known as the mineral halite, has cleavage in three directions. This causes the salt to break into cubes.

You can get an idea of how these weaknesses work by tearing some newspaper. Starting at the top of a page of newspaper, start a tear about an inch from the edge. Hold the top of the page in one hand and the top of the torn strip in the other and pull. The strip should tear easily, all the way to the bottom of the page. The paper that newspapers are printed on have weaknesses that run from the top of the page to the bottom. Now, try using the same method to tear a strip from one side of the paper to the other. You will find that it is much more difficult to get the strip to tear all the way across the page. You are trying to tear across the weaknesses and the tear keeps trying to follow these weaknesses.

While the weaknesses of the newspaper are caused by the way the paper is manufactured, the weaknesses in the salt are part of the crystalline structure.