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What do Diamonds, iron, salt and chocolate all have in common?

What do Diamonds, iron, salt and chocolate all have in common?

Crystals

The simple answer is that they are all crystals! Most people when they think of crystals think of Diamond, Quartz, Rubies and other gemstones. However, there are many more crystals all around us in the world. What makes a crystal a crystal is a repeating structure. Take a look at the classic MC Escher drawing below.

If you look at the pattern you will notice that it is made up of the same unit repeated over and over again (shown by the red shape). A crystal is something made of a repeating structure, just like the Escher drawing shown. In the case of a real crystal this repetition occurs in three dimensions. Therefore anything that has this type of repeating structure is called a crystal. This includes diamonds, metals and chocolate.

Pattern designed by MC Escher. Red box indicates the repeating unit from which the pattern can be made

The crystal structure of chocolate is what is responsible for the shiny nature of dark chocolate and for the crack you get when you break chocolate. If you try cheap or old chocolate then you’ll find that it is not as shiny and doesn’t snap properly, because the structure is less crystalline!

For us, as metallurgists, it is incredibly important to understand the crystal structure of the metal to understand the properties. A good analogy is with lego blocks. By changing the elements (in a process called alloying) that go into the material we can change the crystal structures. This is basically like making different sizes and shapes of lego blocks. By changing the size and shape of the blocks we are able to build different structures with different properties. Therefore, by changing the composition of the alloy we can make changes to the crystal structure and so to the properties of the overall material; allowing us to design new materials with more desirable properties.

 

Image accreditation:

"Brillanten" by Mario Sarto - Self-photographed.

"Chocolate - stonesoup" by jules - chocolate-2

"Iron electrolytic and 1cm3 cube" by Alchemist-hp