The commonest kind of crystalline alumina, α-aluminium oxide, is named corundum. When trace things help it become look crimson it is named ruby, but all other colorations fall under the designation sapphire. Corundum has a trigonal Bravais lattice with a space team of R-3c (variety 167 from the Intercontinental Tables). https://berniem318waj2.bloggazzo.com/profile