Giants in Chihuahua

Silicon single crystalWe take crystals for granted, maybe because they are so common. The Earth’s crust is crystalline, as are our cutlery, and even our bones and teeth are partly crystalline. But crystals are remarkable things. Although most crystalline materials are made of many tiny crystals mushed together (our bones are like this), sometimes huge single crystals can grow. There are crystals in the Naica mine in the Chihuahua state* of Mexico that are over 10 cubic metres in volume. This corresponds to maybe 1030 atoms. And in a single crystal, all atoms are on the same crystal lattice, all 1030 of them here. So the relative positions of pairs of atoms in one corner of the crystal are the same as in the opposite corner over 10 metres or more than 10 billion layers of atoms away. That’s a lot of layers, and presumably they grew one at a time. These big crystals may have started growing before the first civilisations arose in what is now Egypt and Iraq, thousands of years ago. The growth of large perfect crystals can be a slow business.

It is pretty remarkable that atoms can organise themselves into almost perfectly regular layers billions of atoms wide and for billions of layers in succession. But they do. And it is a good job they do. The silicon chips that run our computers, tablets, phones, digital radios, tvs, etc etc, all start out life as a piece of a slice of a large single crystal of silicon like the one in the picture up top.

* Chihuahua is a state in north Mexico, it borders New Mexico and Texas. I think the dogs of the same name may have originally come from there. I never really associate Mexico with small dogs but I think it is true.

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