The most typical sort of crystalline alumina, α-aluminium oxide, is known as corundum. When trace factors enable it to be seem pink it is known as ruby, but all other colorations fall underneath the designation sapphire. Corundum provides a trigonal Bravais lattice with an area team of R-3c (number 167 https://metallography09754.luwebs.com/35562997/everything-about-diamond-paste