Crystals are formed internally by identical units of matter periodically ordered in space, like the atoms of iron (orange) and sulfur (yellow) in this pyrite crystal.
“Build your crystal” is an installation that allows you to see how, using simple cardboard boxes, a crystal is formed by stacking identical units of “integrant molecules” – thus called by René Haüy, who discovered this internal order upon noticing that when he broke a rhombohedron of calcite he obtained other smaller rhombohedrons, and from them other even smaller rhombohedrons… Tiene más información sobre la ordenación periódica de unidades en los cristales en el panel “Cristales: materia ordenada“.
Puede comprobar también que la forma externa de los cristales se debe al orden reinante en su estructura interna y que la misma estructura interna puede crear diferentes morfologías. Compruebe que con estos cubos de cartón, puede crear “cristales” con forma de:
O si desordena todos los cubos, habrá creado un vidrio, un solido amorfo.
To create a crystal, more work, more energy, is needed than to create an amorphous. In an amorphous solid the units, the molecules, are disordered. In a crystal they must be ordered and positioned side by side. The bonds that hold the units together are responsible for doing so.
In order to see how a crystal grows, you can create a crystalline surface with a layer of ordered cubes and a second that partially covers it, as seen in the following figure.
Now imagine that this crystal is growing in a solution, like a salt crystal in a container with seawater. A new box arrives at the surface of the crystal and latches on to it with only one of its six faces. It is highly likely that the water molecules will pull at it to return it to the solution. But it can move over the surface and reach the step, and then it will latch on to the crystal with two of its six faces. It still has four faces that the water molecules will pull on to return it to the seawater. But if it continues moving and reaches the corner, then it will be bonded by three of its six faces. From there it will be difficult to shift it, and when another cube is placed alongside it, then there is no going back. This is how crystals grow. You can find more information on this subject in the panel “How Do Crystals Grow?”.