Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Eileen Gerloff
HOW TO GROW CRYSTALS
For the most part crystals are very easy to grow and make a great science or school project or an activity for the family.
Before we get started letís talk about what a crystal is. A crystal is a mineral found in nature which has an internal structure of a geometric repeating pattern throughout the structure. This pattern will be different for each kind of chemical.
Photos courtesy of Roger Weller
Below is the repeating structure pattern of an alum crystal and the kind of alum used in making crystals.
The easiest and safest crystals to grow are ALUM crystals. Alum can be easily obtained at the grocery store in the spice section. The chemical compound is aluminum potassium sulfate, and is commonly used in canning pickles. http://dictionary.reference.com/browse/Alum?jss=0
Ok, letís get started!
You will need:
2 - 3 Tablespoons Alum
2 clean clear glasses
1 cup boiling water (have an adult help)
Step 1: GROWING YOUR SEED CRYSTAL.
Place 1 cup boiling water into a clean clear glass. Add one tablespoon of Alum at a time and stir until all powder is gone. If there is powder that wonít dissolve pour the liquid into the other clean glass leaving the un-dissolved powder in the bottom of the glass.
Place the glass in a quiet place where it wonít be disturbed and cover it with a paper towel or coffee filter to keep dust out. Check it in 1 to 2 days and you will have seed crystals starting. Let the alum crystal continue to grow for 3 to 6 days UNDISTURBED. At this point pour the liquid off the top of the crystals into a clean clear glass. Then pour the crystals into a paper towel to catch all of them. Select the best crystal to start growing. Tie a thread around the crystal and suspend it into the solution that was poured into the clean glass, with a plastic knife or Popsicle stick.
The small crystals were grown for 2 days the large one was grown for 2 weeks.
While the crystal is growing additional crystals may start to grow and interfere with your large crystal. Simply remove the crystal from the solution and pour in into a clean glass and suspend your crystal again into the solution.
If crystals are kept in a dry air tight contain they will last a while without change. To seal your crystal coat it with a clear acrylic paint. This may melt the outside layer but will encase and protect it. Have fun!
In order to grow salt crystals that look cool they need a support system to grow on otherwise they look like someone forgot to wash the dish. For this experiment you need salt that is used for canning pickles (found in the canning section at the grocery store or Wal-Mart). This salt is sodium chloride that is very fine grained and is very pure; it has no iodine or other additives.
Stir Ĺ to ĺ cup salt into one cup hot tap water. Pour off the super saturation solution and leave any undissolved crystals in the bottom of first glass. Put some tissue in the solution to support the salt crystals and wait for the crystals to grow. You could form the structure into a word or your initials.
The picture below is after 2 weeks of undisturbed growth. Notice that the salt formed all around the glass.
Salt is a necessary chemical our bodies need in order to live. Salt comes from deposits in the earth. The oldest salt mine in the world is located in Hallstatt, Austria. It has been in production for 7,000 years and claims to have been used during the Stone Age. Originally salt was mined as rock salt (halite) until they developed a process of flooding the mine with water, allowing the salt to dissolve into a brine solution, and pumping the water out of the mine. Transported to another location where the water is evaporated and turned into what we know as table salt. http://h2g2.com/dna/h2g2/A61943493
Another familiar salt mine is Saltsburg, Austria. I was fortunate enough to visit this mine several years ago and it was very entertaining as well as informative. It is an underground mine. You start the tour by putting on protective clothing which includes a leather seat guard. Then you get on a mine train and go into the mine for a short ride. Then you straddle a giant log slide that has been polished by miners and visitors over many years going down to the lower levels of the mine. It is believed that this mine has been operated since 400BC. You are able to see different shapes the salt has formed as you walk through the tunnels. Then you are loaded on to a raft and pulled across an underground lake. They are kind enough to let you use elevators to get out instead of climbing out.
COPPER SULFATE CRYSTALS
Copper Sulfate crystals are equally as easy to grow but copper sulfate is poisonous and is used to kill tree roots in sewer lines. Purchase it at any hardware store in the pesticide section. If you canít find it ask for it by name and someone can help you find it.
Start out by making a super saturation solution. Start with 1 cup of water in a clear jar or glass. Stir in about ĺ cup of copper sulfate. If it all dissolves add a teaspoon more at a time, until no more crystals will dissolve. There will be some crystals in the bottom of the jar. Pour off the liquid, leaving any undissolved crystals behind.
Place it in a safe area that will not be
disturbed and cover it with a paper towel to keep the dust out. Within a hour
or two you will have a seed crystal. You can wait over night for the crystal to
get bigger, but if you wait too long the crystals will cement themselves
together at the bottom of the glass. Tie a thread around the best looking
crystal and suspend it into the middle of the solution. Again let it sit
covered and in a week or two a large crystal will be formed.
After two weeks the crystal is finished. To preserve it you can put a light coat of clear acrylic paint. http://chemistry.about.com/od/crystalrecipes/a/coppersulfate.htm
Photos of crystals by Roger Weller, http://skywalker.cochise.edu
Structure of alum crystals, http://demonstrations.wolfram.com/
Definition of Alum, http://dictionary.reference.com/browse/Alum?jss=0
Definition of Pickling salt compound, http://www.wisegeek.com/what-is-pickling-salt.htm
Hallstatt mine, http://h2g2.com/dna/h2g2/A61943493
How to grow copper sulfate crystals, http://chemistry.about.com/od/crystalrecipes/a/coppersulfate.htm