Zimmerman's Science Class |
structures that are formed from a regular repeated pattern of connected atoms
or molecules. Crystals grow by a process termed nucleation. During
nucleation, the atoms or molecules that will crystallize (solute) are
dissolved into their individual units in a solvent.
The solute particles contact each other and connect with each other. This
subunit is larger than an individual particle, so more particles will contact
and connect with it.
this crystal nucleus becomes large enough that it falls out of solution
(crystallizes). Other solute molecules will continue to attach to the surface
of the crystal, causing it to grow until a balance or equilibrium is reached
between the solute molecules in the crystal and those that remain in the
a saturated solution.
a garden or grow a seed crystal.
In order to
grow a crystal, you need to make a solution which maximizes the chances for
the solute particles to come together and form a nucleus, which will grow into
your crystal. This means you will want a concentrated solution with as much
solute as you can dissolve (saturated solution). Sometimes nucleation can
occur simply through the interactions between the solute particles in the
solution (called unassisted nucleation), but sometimes it's better to provided
a sort of meeting place for solute particles to aggregate (assisted
nucleation). A rough surface tends to be more attractive for nucleation than a
smooth surface. As an example, a crystal is more likely to start forming on a
rough piece of string than on the smooth side of a glass.
It's best to
start your crystals with a saturated solution. A more dilute solution will
become saturated as the air evaporates some liquid, but evaporation takes time
(days, weeks). You will get your crystals more quickly if the solution is
saturated to begin with. Also, there may come a time when you need to add more
liquid to your crystal solution. If your solution is anything but saturated,
then it will undo your work and actually dissolve your crystals! Make a
saturated solution by adding your crystal solute (e.g., alum, sugar, salt) to
the solvent (usually water, although some recipes may call for other
solvents). Stirring the mix will help to dissolve the solute. Sometimes you
may want to apply heat to help the solute dissolve. You can use boiling water
or sometimes even heat the solution on the stove, over a burner, or in a
Crystal Garden or 'Geode'
If you just
want to grow a mass of crystals or a crystal garden, you can pour your
saturated solution over a substrate (rocks, brick, sponge), cover the setup
with a paper towel or coffee filter to keep out dust, and allow the liquid to
On the other
hand, if you are trying to grow a larger single crystal, you will need to
obtain a seed crystal. One method of getting a seed crystal is to pour a small
amount of your saturated solution onto a plate, let the drop evaporate, and
scrape the crystals formed on the bottom to use as seeds. Another method is to
pour saturated solution into a very smooth container (like a glass jar) and
dangle a rough object (like a piece of string) into the liquid. Small crystals
will start to grow on the string, which can be used as seed crystals.
Growth and Housekeeping
If your seed
crystal is on a string, pour the liquid into a clean container (otherwise
crystals will eventually grow on the glass and compete with your
crystal), suspend the string in the liquid, cover the container with a paper
towel or coffee filter (don't seal it with a lid!), and continue to grow your
crystal. Pour the liquid into a clean container whenever you see crystals
growing on the container.
selected a seed from a plate, tie it onto a nylon fishing line (too
smooth to be attractive to crystals, so your seed can grow without
competition), suspend the crystal in a clean container with saturated
solution, and grow your crystal the same way as with seeds that were
originally on a string.
were made from a water (aqueous) solution will dissolve somewhat in humid air.
Keep your crystal beautiful by storing it in a dry, closed container. You may
wish to wrap it in paper to keep it dry and prevent dust from accumulating on
it. Certain crystals can be protected by being sealed with an acrylic coating
(like Future floor polish), although applying the acrylic will dissolve the
outermost layer of the crystal.