Calcium carbonate crystals can take any of a number of forms. You can grow your own crystals that will resemble either the clear needle-like calcium carbonate prisms found naturally around hot springs or the delicate, lace-like branching structures found in caves and mines (cave flowers). The mineral CaCO3 is known as aragonite when it occurs naturally. Calcium carbonate also takes other forms as vaterite and calcite crystals, but you’d need to control the pH (acidity of the solution) to see these forms.
Materials for Calcium Carbonate Crystals
This is a super-simple project, since you only need two materials!
- dolomite rocks
- household vinegar (dilute acetic acid)
If you haven’t collected any dolomite rocks or can’t find them, dolomite is also commonly sold in garden stores in powdered form. You can also get dolomite at Amazon. You can use powdered dolomite just fine, but you’ll want to provide a growing surface to support crystal growth. An old piece of kitchen sponge works great since it offers a large surface area. If you want a more natural-looking crystal, you could grow the crystals on a rock.
Let’s Grow Crystals!
If you have a dolomite rock, rinse it off to remove any dirt and debris and let it dry.
Place your dolomite rock in a container. Try to choose one that’s just a bit larger than the rock, to reduce the amount of vinegar you need. If you’re using powder, place your growing rock or piece of sponge in a container and heap the powder on top of it.
Pour vinegar around the rock or sponge, but don’t completely cover the surface. You want to leave exposed space at the top.
Set the container someplace where it won’t be disturbed. Be patient. In about a day, the calcium carbonate crystals will start to grow at the liquid line.
When you’re pleased with the crystal growth (usually 5 days to 2 weeks) you can remove the crystals to observe or display them. Alternatively, you could just wait for all the vinegar to evaporate.
If you used pure calcium carbonate, your crystals would be clear or white. Using dolomite as the source, your crystals will be colored. The color depends on other compounds found in the mineral. Brown, green, and gray are common colors.
Dolomite, Aragonite, and More
Dolomite is a sedimentary rock made of calcium carbonate. Aragonite is a crystalline form of calcium carbonate.
Calcium carbonate also takes other forms. It’s commonly found in biological systems, especially in the ocean. Sea shells and pearls also consist of this mineral.
Time Lapse Video of Calcium Carbonate Crystal Growth
Would you like to see what to expect? Here’s a time lapse video of calcium carbonate crystals growing from a “popcorn” rock: