An ettringite sample extracted from Scawt Hill was analysed by C. E. Tilley, the crystal was 1.1 x 0.8 0.5 mm, with specific gravity of 1.772±0.002, the density was determined by immersing the sample in a solution of carbon tetrachloride mixed with bromoform. The crystal showed five prism faces of the form "m" {100} and a small face "a"{110}, with no pyramidal or basal faces, upon x-ray diffraction a Lauer gram along the "c"-axis revealed a hexagonal axis with vertical planes of symmetry, this study showed that the structure has a hexagonal and not a rhombohedral lattice. further studies conducted on synthetic ettringite by use of x-ray and powder diffraction confirmed earlier assumptions and analyses.