Calthemite coralloids (also known as popcorn), can form on the underside of concrete structures and look very similar to those which occurs in caves. Coralloids can form by a number of different methods in caves, however on concrete the most common form is created when hyperalkaline solution seeps from fine cracks in concrete.  Due to solution evaporation, deposition of calcium carbonate occurs before any drop can form. The resulting coralloids are small and chalky with a cauliflower appearance.