Popcorn Rocks

Popcorn Rocks are an excellent tool for teaching chemistry and/or geology… or,  just to have around for plain fun. Submerge this limestone rock in white distilled vinegar and watch as a crystal garden grows over the next few weeks. Popcorn Rocks makes a great long term educational project for the classroom or those aspiring young geologists at home.

Recently, an alert visitor to our website submitted this great explanation for what is happening in the popcorn rock experiment: “the calcium carbonate present in the rock is dissolved by the acetic acid in the vinegar to form calcium acetate in a water solution (water is produced as part of this reaction and is also present in the vinegar). You can see the creation of carbon dioxide gas bubbles as this happens. The rock contains fine veins perhaps hollowed out by the action of the acid. The water slowly evaporates, the calcium acetate thus concentrates and wicks up these veins through capillary rise. By further slow evaporation of the water the calcium acetate crystals grow. Such crystal growth processes are not mysterious, but rather common. What is uncommon is the nature of the popcorn rock that facilitates this.”

Ages 3+