Corundum is the most interesting mineral on the planet. It is possible to find corundum in almost any color in nature, and even with a color change effect depending on lighting (the so-called alexandrite effect).
 

There are many colors of corundum supplied by RG Crystals. All the synthetic corundum colors were assigned certain numbers for the sake of simplicity and to avoid mix-ups during repeat orders. This numbering system is common and considered international. All the colors listed above may vary in terms of density. So the color may have the same name but a different number.