Green growth covering stone is commonplace, and such growth will often be associated with deterioration of the stone's surface. Closer examination reveals that the growth can be algae, lichen, mosses, and higher plants, and it is often a matter of dispute whether or not the growth causes physical deterioration of the stone. Energy-dispersive x-ray analysis (EDX) was used to determine the amounts of calcium in deteriorated stone and in the plants growing there. Results have shown that the amount of calcium in the attacked stone had decreased and that the calcium in the plants had increased, indicating that the erosion of the stone was caused biologically.