Crystal Formation Task
Crystals can grow in different shapes and sizes depending on the internal symmetry of the crystal, and the relative growth rates along the various directions of the crystal. For example if you have equally perpendicular axes, a, b, and c. Suppose the crystal grows at equal rates along a, b, and c, then the crystal shape will be a cube. Suppose a different crystal grows fast in the a and b direction, but very slowly in the c direction. The crystal will then grow as thin plates with the face of the plate being perpendicular to c.The presence of different chemicals causes the variety of colors to different crystals.
some different types of crystals include cubic - not always cube shaped, hexagonal - six-sided prisms, trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division, tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms, monoclinic - like skewed tetragonal crystals, often forming prisms and double pyramids, triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.
Because warmth is the key to forming crystals; the jar's surroundings should be warm also for optimum crystal growth. Warm air temperature helps water evaporation, causing the crystals to grow more quickly. Crystals will still grow in cooler temperatures, but it will take much longer for the water to evaporate. Crystal growth also requires light. Again, the crystals will eventually grow in the dark, but it will take a very long time. Light evaporates water as heat does; combine them by placing your jar on a warm, sunny windowsill and you should have crystals in a few days.
two 250ml beakers
stirring rod, tweezers, tongs, spatula or plastic spoon
fine nylon thread
watch-glass or paper hat
smart phone or digital camera
diary or log book
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. 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 next day, 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. 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.
During the holidays
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. Once a week record in your diary the level of the solution in the beaker and if possible, without disturbing your crystal, take a picture of it close to a ruler so that you can estimate how much it has grown. Try and avoid disturbing crystals during the growth phase as this may induce additional crystals to grow.