Crystals are solids that form by a regular repeated pattern of molecules connecting together. In some solids, the arrangements of the building blocks (atoms and molecules) can be random or very different throughout the material. In crystals, however, a collections of atoms called the Unit Cell is repeated in exactly the same arrangement over and over throughout the entire material.


Because of this repetitive nature, crystals can take on strange and interesting looking forms naturally. When we grow crystals we are separating all the building block molecules into individual units in water and letting them fall naturally into their appropriate place in the repetitive structure as the water evaporates.


Through these pages you can learn what types of crystals there are, why different crystals have different shapes and sizes,  find out how light affects the color of a crystal and how crystals form and how they grow. Making Crystal Gardens is fun and rewarding, so we've left you a few ideas a


Crystals start growing by a process called "nucleation". Nucleation can either start with the molecules themselves (we'll call this unassisted nucleation), or with the help of some solid matter already in the solution (we'll call this assisted nucleation).


When molecules of the "solute" (the stuff of which you want to grow crystals) are in solution, most of the time they see only solvent molecules around them. However, occasionally they see other solute molecules. If the compound is a solid when it is pure, there will be some attractive force between these solute molecules. Most of the time when these solute molecules meet they will stay together for a little while, but then other forces eventually pull them apart. Sometimes though, the two molecules stay together long enough to meet up with a third, and then a fourth (and fifth, etc.) solute molecule.


Most of the time when there are just a few molecules joined together, they break apart. However, once there becomes a certain number of solute molecules, a so-called "critical size" where the combined attractive forces between the solute molecules become stronger than the other forces in the solution which tend to disrupt the formation of these "aggregates". This when this "protocrystal" (a sort of pre-crystal) becomes a nucleation site. As this protocrystal floats around in solution, it encounters other solute molecules. These solute molecules feel the attractive force of the protocrystal and join in. That's how the crystal begins to grow.


It continues growing until eventually, it can no longer remain "dissolved" in the solution and it falls out (as chemists like to say) of solution. Now other solute molecules begin growing on the surface of the crystal and it keeps on getting bigger until there is an equilibrium reached between the solute molecules in the crystal and those still dissolved in the solvent.


Pretty much the same thing happens as in unassisted nucleation, except that a solid surface (like a stone, or brick) acts as a place for solute molecules to meet. A solute molecule encounters the surface of a stone, it adsorbs to this surface, and stays on it for a certain time before other randomizing forces of the solution knock it off. Solute molecules will tend to adsorb and aggregate on the surface. This is where the protocrystal forms, and the same process as described above happens.


You can probably see why, from what I wrote above, crystals grow fastest in a solution in which the concentration is near saturation. If there are more solute molecules in a given volume, then there is more of a chance they will meet one another. You also don't want to heat up the solution because that acts as the major randomizing force in solution which causes the aggregates of molecules to break up.

long with other Crystal growing recipes you can try - such as growing Crystals on a String - that with a little patience and imagination you could suspend from the ceiling as a mobile!