Crystals form on porous surfaces like rocks after evaporation leaves chemical deposits behind.
Crystallization occurs when the atoms, molecules or ions of a solid are arranged in a repeating pattern that extends in all three spatial dimensions. Crystals form in a variety of ways and from a range of substances. Experiments with crystals can examine how crystals form from different materials.
String Crystals
Add a teaspoon of table salt, sugar or Epsom salts to a cup of boiling water. Continue adding more of the substance until it no longer dissolves. Pour the solution into a glass. Tie one end of a string around the center of a pencil and the other end around a paper clip. Lay the pencil over the glass with the string hanging in the solution. The crystals will form after a few days. As the solution evaporates, the crystals will grow larger. Experiment with different starting chemicals and compare the crystals formed by each.
Seed Crystals
Experiment with seed crystals, which form as a solution evaporates. Pour 20 oz. of water into a saucepan and add 4 oz. of alum powder. Heat slowly and continue adding alum until it no longer dissolves. Pour a small amount of the solution into a saucer and the rest into a jar. Add one tbsp. of alum powder to the jar and cover it with a cloth. Once the solution has evaporated from the saucer, you will have crystals. Choose the biggest crystal as your seed. Tie a thread around the crystal and wind the other end around a pencil. Hang the seed in the jar solution, resting the pencil over the top. Watch the seed crystal grow over a period of about two weeks. Repeat the experiment with another chemical substance such as salt or sugar and observe the different crystals that form.
Crystal Garden
A salt crystal garden experiment demonstrates how crystals form on rocks and other porous materials. Mix 4 tbsp. each of salt, liquid bluing, water and ammonia. Place small pieces of porous rock such as charcoal or clay into a glass or plastic bowl. Pour the mixture over the rocks. Crystals will form in about three days. On the third day, mix more salt, bluing, ammonia and water, and add this mixture to the rocks to keep the crystals growing. Do not drip new solution onto crystals already formed. The porous rocks draw the solution up, water evaporates on the surface, and solid chemicals are left behind to form the crystals, which can eventually grow over the sides of the bowl.
Stalagmites and Stalactites
Ground water containing calcium carbonate moves through the walls of a cave and, as it evaporates, the ceiling forms deposits called stalactites. Water that drips onto the cave's floor will build similar deposits called stalagmites. Experiment with this process to see how these crystals form. Fill two jars about 3/4 full of hot water and place them on a tray. Add Epsom salt -- magnesium sulphate -- to one jar until it no longer dissolves. Do the same in the other jar, but add washing soda -- sodium carbonate -- instead of Epsom salt. Attach a washer to each end of an 18-inch cotton strip. Place one end of the strip into each jar. Position the jars so the strip hangs one to two inches from the tray. Set the tray in an area where it won't be disturbed. In about one week, stalactites and stalagmites will begin to grow.
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