Abstract: Junitoite, CaZn2Si2O7·H2O, is orthorhombic, space group Area2, with a = 12.510, b = 6.318, c = 8.561 Å, Z = 4. The structure, determined on the basis of three-dimensional Mo-Kα intensity data for 745 reflections refined to R = 0.10. The structure consists of ZnO4 tetrahedral chains along b joined by Si2O4 groups along a and c to form a three-dimensional network. Ca occurs in distorted CaO5(H2O) octahedra. The structure shows similarities to hemimorphite and Ca-Zn silicates but represents a unique tetrahedral framework.