Parthéite, CaAl₂Si₂0₈.2H₂0, occurs with prehnite, thomsonite, augite in rodingitic rocks from an ophiolitic zone in the Taurus Mountains, Southwest Turkey. The name is in honour of Professor Erwin Parthé, of the "Laboratoire de Cristallographie aux rayons X" at the University of Geneva, Switzerland. Both mineral and name have been approved by the Commission on new Minerals and Mineral Names of the International Mineralogical Association. Electron microprobe analysis has shown the uniform distribution of the major elements and the absence of other components. X-ray powder diffraction data are from a Gandolfi camera. The crystal system is monoclinic, and the cell parameters are: a=21.59; b 8.78; c=9.31 Å and β=91.47°. The probable space group is C2/c. The major X-ray diffraction lines occur at 10.78 (100)(200); 8.11 (80)(110); 6.10 (70)(111); 3.74 (50)(22l); 3.60 (40)(312)(511); 3.19 (40)(022); 3.04 (30)(222) and 2.90 (30)(130)(113) Å. The mineral is fibroradiated or more rarely observed as distinct crystals, varying in size between 0.1 and 0.3 mm. The measured density is 2.39 g/cm³, the calculated density being 2.37 g/cm³. The refractive indices are: α=1.547; β=1.549; γ= 1.559(±0.001), optically positiv, 2Vγ =48°. The crystallisation of parthéite is related to metasomatic processes of rodingitisation.