The commonest form of crystalline alumina, α-aluminium oxide, is recognized as corundum. When trace factors ensure it is surface crimson it is named ruby, but all other colorations tumble underneath the designation sapphire. Corundum has a trigonal Bravais lattice with a space group of R-3c (variety 167 from the Intercontinental https://lanthanumcarbonate21086.atualblog.com/41156627/details-fiction-and-diamond-paste