Corundum is 9 on the Mohs scale, harder than anything natural except diamond. The first laser, built by Theodore Maiman in 1960, was a rod of synthetic ruby with silvered ends. The structure is the same as hematite’s: oxygens in close-packed layers with aluminium in two-thirds of the octahedral holes between them.
Research Elements Compound · Al2O3 One unit cell, the smallest block that repeats in every direction to build the whole crystal. Atoms on its faces, edges and corners are shared with the neighboring cells. Farther atoms are drawn fainter. Atom positions from the Crystallography Open Database entry 9008081 (Newnham, R. E.; de Haan, Y. M., 1962). In metamorphic rocks rich in aluminium and poor in silica, such as marble and gneiss, and in the river gravels that weathered out of them. Red corundum is ruby, from Mogok in Myanmar and Montepuez in Mozambique; every other color is sapphire, from Sri Lanka, Kashmir, Madagascar and Montana. A trace of chromium makes the red, iron and titanium the blue. Gem corundum mostly comes from gravels, dug by hand or with small excavators and washed in sluices so the heavy crystals stay behind. Emery, an impure corundum, is quarried on Naxos and in Turkey for sandpaper and grinding wheels. Almost all other corundum is made: aluminium oxide from bauxite is fused in electric arc furnaces for abrasives, or melted drop by drop in a flame and grown into boules by the Verneuil process, invented in 1902, for watch jewels, lasers and sapphire windows.Corundum
Elements
Crystal structure
Cell: a = b = 4.7589 Å, c = 12.991 Å, angles 90°, 90° and 120°
Space group: R -3 c :HWhere it's found
How it's mined
Notes