Fossil Fern like any other fossilized or petrified animal or plant material, begin petrifying by becoming burried in thick layers of sediments. This excludes oxygen which prevents decay. A number of mineral substances, such as calcite, pyrite, marcasite and others can cause petrifaction, but by far the most common is silica. Solutions of silica dissolved in ground water infiltrate the buried organic materials and through a complex chemical process are precipitated and left in the individual cells of these materials. This pendant is 38 x 25 mm (1.52" x .98") Chain not included.