Vuagnatite, CaAl(OH)SiO₄, occurs with prehnite, hydrogrossular, vesuvianite, and chlorite in rodingitic dykes from an ophiolitic zone in the Taurus Mountains, southwest Turkey. The name is for Professor Marc Vuagnat, of the Department of Mineralogy of the University of Geneva, Switzerland. Electron microprobe analysis has shown the uniform distribution of major elements and the absence of other components. X-ray powder diffraction data are from Gandolfi and Hägg-Guinier cameras. The crystal system is orthorhombic, and the cell parameters are: a= 7.055(6), b = 8.542(7), and c = 5.683(5) Å. The space group is P2₁2₁2₁. Vuagnatite is isotypic with conichalcite, CaCu(OH)AsO₄. Prominent X-ray diffractions occur at 2.993, 2.635, 2.517, 2.391, and 2.453 Å. Crystals are generally anhedral, varying in size between 0.03 and 0.5 mm. The measured density is 3.20-3.25 g/ cc, the calculated density being 3.42 g/cc. This difference is due to difficulties in getting material free of inclusions. The refractive indices are: α = 1.700, β = 1.725, γ = 1.730; optically negative, 2V = 48° . The crystallization of vuagnatite is related to metasomatic processes of rodingitization.