Grow Your Own Multicolor Mineral Crystal Specimen

Natural minerals need millions of years to form, but you can make a homemade mineral in just a few days using inexpensive ingredients you can get at a home supply store. The chemicals grow different colors of crystals, which look like a geological specimen. The result is pretty enough to showcase at home or in the lab.

• alum or chrome alum
• copper sulfate
• borax or boric acid
• water
• food coloring (optional)
• rock or other material for a base

Regular white alum is sold as a kitchen spice. If you use this alum, you'll want to add food coloring to grow colored crystals or you can stick with the natural clear crystals. Chrome alum (also known as chromium alum or potassium chromium sulfate) is available online and grows natural purple crystals. If you have both chemicals, you can mix them to produce natural lavender-colored crystals.

Copper sulfate grows naturally blue crystals. It is sold either as a pure chemical online or as a root killer at a home supply store. Check the label to make sure copper sulfate is the ingredient. The product will look like a blue powder or granules.

Boric acid is sold as an insecticide (roach killer) or disinfectant powder. Borax is sold as a laundry booster. The white powder of either chemical produces delicate white crystals.

Growing a homemade mineral specimen is a multi-step process. You'll grow one layer of crystals on a rock, let the specimen dry, then grow another layer of a different chemical, let it dry, and grow the third layer to complete the project.

First, find a rock and a container just large enough that you can add liquid to cover the rock completely. You don't want too big of a container or you'll have to make up a lot of each crystal solution.

Make up the crystal growing solutions one at a time, as you need them. In all cases, the procedure for preparing the solution is the same.

1. Dissolve as much chemical as you can in boiling hot water. Add food coloring, if desired.
2. Filter the solution through a paper towel or coffee filter to remove any sediment.
3. Allow the solution to cool slightly so you don't burn yourself and don't accidentally dissolve any pre-existing crystals (for the second and third crystal sets).
4. Place the rock or other substrate in a container. Pour the solution into the container until the rock is covered.
5. Allow crystals to grow overnight or for a couple of days (until you are pleased with them). Then carefully remove the rock and place it on a paper towel to dry. Empty the container of solution and let it dry.
6. When the rock is dry, return it to the empty container and add the next crystal solution.

While you can grow the crystals in any order, my recommendation is to start with the alum, followed by the copper sulfate, and finally the borax. In any case, I'd do borax last because the crystals are relatively fragile.

Once the "mineral" specimen is complete, allow it to air dry. Once it is dry, you can display it. Over time, changes in the humidity of a room will alter the appearance of the crystals. If you wish to store the crystals, gently wrap them in paper to help keep the humidity stable.

• 5 tablespoons alum
• 1 cup very hot water

Copper sulfate saturation is highly dependent on water temperature. Determine how much water you need to fill your container. Heat it in a kettle or microwave until it boils. Keep stirring in copper sulfate until no more will dissolve. There will be undissolved material in the bottom of the container that you can filter out using a paper towel.

Stir boric acid or borax into very hot tap water until no more will dissolve.

If three colors isn't enough for you, you can add delicate needle-like crystals of Epsom salts or red potassium ferricyanide crystals.