Metaminct minerals exist in an unusual noncrystalline condition which is observed in at least 50 minerals. The term is applied to certain complex minerals containing U and/or Th which, in the course of time, have passed from a truly crystalline state to an amorphous state. The state is thought to result from radiation damage caused by bombardment by alpha particles from disintegrating atoms of U, Th, and their decay products. The state is found in oxides, phosphates, and silicates. The general formula for metaminct minerals is AxByCz, where A = Ce, Y, Er, La, U, Th, Ca, Na, Fe⁺², Mn⁺², Pb⁺², ..., B = Nb, Ta, Ti, Zr, Fe⁺³, and C = O, OH, F, etc. Metaminct minerals have essentially the same concentration as the original mineral. Often, however, changes in physical properties occur, such as becoming X-ray amorphous, optically isotropic, and more susceptible to chemical change. The also often become thermoluminescent upon heating, which also causes them to turn lighter in color.