The mineral ettringite has a structure that runs parallel to the "c" axis -the needle axis-; in the middle of these two lie the sulfate ions and H2O molecules, the space group is "P31c". Ettringite crystal system is trigonal, crystals are elongated and in a needle like shape, occurrence of disorder or twining is common, which affects the intercolumn material. The first X-ray study was done by Bannister, Hey & Bernal (1936), which found that the crystal unit cell is of a hexagonal form with a=11.26 and c=21.48 with space group P63/mmcand Z=2. From observations on dehydration and chemical formulas there were suggestions of the structure being composed of Ca2+ and Al(OH)63−, were between them lie SO42− ions and H2O molecules. Further X-ray studies ensued; namely Wellin (1956) which determined the crystal structure of thaumasite, and Besjak & Jelenic (1966) which gave affirmation of the structure nature of ettringite.