Taking over Australia. One science classroom at a time.
The Need-To-Know About Crystals
In scientific terms, a crystal is a geometrically regular product formed by a
uniform repetitive pattern of molecules. In casual terms, it is a pretty
Many things can be used to create crystals but the more common substances are potassium alum, sodium acetate, calcium chloride and copper acetate. In nature, crystals such as quartz, agate and citrine among others are formed due to water, temperature and pressure. Household items such as string and charcoal can be used to grow crystals from.
There are many different
types of crystals but they are classed according to their structure as either covalent,
metallic, ionic or molecular. A chemical process takes
place within the solution as over time the molecules come together and harden
into a crystal lattice structure. Crystals grow in different shapes and sizes
depending on the environment they’re in, the chemical they’re grown from and
the arrangement of the crystal structure. When light enters a crystal
it is bent, refracted off the crystal’s many facets causing total internal
reflection. The best conditions for crystal growth are cool, draught-free locations that are always at a constant temperature.
Creating a Crystal:
2 250mL beakers
25g potash alum
Place approximately 25 g of potash alum in a beaker (250 ml or bigger) and add
approximately 170 ml of hot water.
Stir the mixture until all the crystals have dissolved. The solution may have a slightly cloudy or milky appearance due to impurities in the technical grade of alum used.
(NOTE: don’t use all the alum you have been given – keep a few crystals back in reserve in case you need to “seed” the solution later.)
Filter the warm solution through a filter funnel (in which filter paper has been inserted) into another clean beaker.
Cover the beaker of solution with the watch glass or fresh filter paper and set aside in a cool sheltered place and allow it to stand undisturbed overnight.
(The first beaker and funnel can be washed and dried and the residue and filter paper used for filtration discarded.)
Observe the beaker of solution. The bottom should have become covered with a layer of smallish crystals which formed spontaneously as the solution cooled.
Carefully decant (pour off) the clear solution above the crystals into a clean beaker and set it aside for later, leaving the crystals behind in the other beaker. If for any reason, no crystals have formed after leaving the solution to stand overnight, the solution can be “seeded” by adding a crystal from the original alum.
Let it stand overnight again and observe the formation of crystals. Alternatively, if nothing has happened, crystal growth may also be induced by scratching the bottom of the glass beaker with a glass stirring rod.
From the bed of crystals, one good symmetrical crystal or group of crystals needs to be selected to act as “seed” for your big crystal. Using a plastic spoon, spatula, tongs or tweezers, transfer the selected crystal to the beaker containing the decanted solution, trying to place it centrally in the beaker.
A good technique to promote uniform growth is to suspend the crystal with a nylon thread tied round a stirring rod or pencil resting on the rim of the beaker. This step is not essential, however, and good a crystal can usually be obtained just by leaving the crystal on the bottom of the beaker.
Take a picture (if possible) of the crystal, preferably close to a ruler so that you can
measure its size, and mark the level of the liquid in the beaker. Record the
date in your diary.
Cover the solution with a loose-fitting paper hat that permits water to evaporate slowly whilst keeping out dust.
Allow the solution to stand in a draft free location, not in direct sunlight or near a heater. The aim is to keep the temperature as constant as possible.
Crystal Word Search Worksheet
And now we wait . . . (a photo gallery)
The final product! (photo gallery)
In conclusion . . .
At first it seemed that my crystals weren’t growing at all but by the end of the first week of holidays it was evident that something was definitely even if the process was invisible to the naked eye. After a week or so they had grown approximately half a centimetre in length. I didn’t measure the liquid levels of the beaker but by the end of the experiment only a centimetre of solution remained. One crystal grew to the length of 2.5 cm and width of 1.5 cm wide while the other was approx. 2.2 cm long and 2 cm wide. The artwork demonstrates the chunky shape of the crystals, rounded with a few sharp corners and emphasises its rough textured surface.