The space symmetry of prehnite, a mineral which occurs in cavities and veins within skarn from the Tieshan iron mineral deposit, Daye, Hubei province, central China, has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale. Our results confirm that natural prehnite may belong to space group Pncm. The unit-cell parameters of the prehnite investigated ( a = 0.458 nm, b = 0.555 nm and c = 1.853 nm) have been calculated using the multicrystal diffraction rings of gold, the internal standard.