Just getting interested in this stuff. People are saying I should crystallize salt, for example. What substances besides salts form a crystal structure?
Maybe to focus more on the question: what kinds of things can you make crystals from:
Typically a pure element or an inorganic or organic compound can be made in crystalline form. It might be a fine powder or small granular crystals. If grown under controlled conditions, you could get large crystals. If it is a gas or liquid at room temperature, it could perhaps solidify to a crystalline form at lower temperatures.
On the other hand, an impure, indeterminate, or polymeric material, or a mixture of compounds, very seldom will form crystals. Still, there are exceptions. Inorganic salts often crystallize from water solution as "hydrates" - with extra water molecules in the crystal lattice of the salt. Other solvents also sometimes co-crystallize with inorganic or organic substances. Neutral compounds can co-crystallize together as clathrates, such as methane hydrate - a crystalline structure containing both methane and water that forms at high pressures and low temperatures.
Even a complex or high molecular weight substance, such as an enzyme or virus particle can form crystals. In the realm of nanotechnology, new materials are being engineered specifically to aggregate into crystal-type structures.
Crystallization in the chemical sense, as previously noted by Nicolau Saker Neto in comment form, is when a solid forms "with a regular atomic lattice".
Ionic compounds such as salts (e.g. NaCl, KCl) would be my first choice, but there might be others I don't know about.
The easiest method I know to do this is by supersaturating.
- Fill a container (such as a cup or a beaker) with water or other suitable solvent.
- Add salt (or other solute) while stirring until the solution becomes saturated and there is a noticeable amount of undissolved solute at the bottom of the container.
- Heat the solution. This increases the solubility of the solute because the particles move farther apart when at a warmer temperature. This is due to the fact that heat and particle motion are linked. This allows a greater amount of solute to dissolve.
- Keep stirring to make sure the solute that was previously collected at the bottom of the container is fully dissolved
- Allow the solution to cool. This reduces the solubility and the solute will crystallize.
Salt is an easy example. Add more salt to water until it can't dissolve anymore, heat it, wait for it to cool, and you will have your salt crystal.