Earth Science Lesson on Growing Crystals
Procedure for Growing Crystals
- White sugar, table salt or Epsom salts (magnesium sulfate, available in supermarkets or drug stores).
- Microwave or hot plate to heat water.
- Clear glass jar.
- Pencil or popsicle stick.
- String (preferably rough cotton rather than smooth nylon).
1. Heat the water in a microwave or on a hot plate until it is nearly boiling.
2. Add sugar, table salt or Epsom salts to the water and stir vigorously to dissolve. Continue adding the solid until no more will dissolve even with stirring, and particles begin to accumulate on the bottom of the container. You will need to add a lot of solid in order to get a saturated solution. If you are using sugar, it will require about two cups of sugar to one cup of water, and the solution will become quite thick and syrupy. If you are using Epsom salts or table salt, it will require about one cup of salt to one cup of water.
3. Pour the saturated solution into a clear glass jar.
4. Tie a few inches of string to a pencil or popsicle stick and lower the string into the jar. Lay the pencil or popsicle stick across the top of the jar so that the string hangs down into the liquid. You may tie a paper clip onto the bottom of the string to hold it down into the liquid. The rough string will give the newly-forming crystals something to attach to.
5. Set the jar in a place where it will not be moved or disturbed for several days, such as on a window sill. if desired, put a paper towel or coffee filter over the top of the jar to keep dust from getting in.
Have students observe the jar every day. Small crystals should begin to form on the string. The crystals will grow larger over the next several days and will continue to grow as the water in the jar evaporates.
Other Ideas for Growing Crystals
In addition to growing crystals in a jar, which can take up to two or three weeks, smaller crystals can be grown quickly by pouring some of the saturated salt or sugar solution onto black construction paper in a shallow container such as a saucer. The crystals will form on the paper as the water evaporates, and the black background will make them more visible. The saturated solution can also be poured over a rough substrate such as a sponge, for the crystals to attach to.
To encourage growth of a large crystal, start out with a seed crystal. You can pick one of the larger crystals from those grown on the shallow plate to use as a seed crystal. Tie a thread onto a pencil or popsicle stick and tie the seed crystal to the other end. Carefully lower the seed crystal into a jar containing a cool saturated solution of the same material as the seed crystal (sugar or salt.)