Several other well known gemstones, including diaspore, sapphire, garnet and spinel may also change color as a function of the light source but the color change of top alexandrites is distinctive and attractive under any light conditions.
An aluminum oxide, it occurs as shapeless grains and masses (emery), rhombohedral crystals. Ruby contains traces of chromium oxide, when red and Fe2O3, which modified the color. The color of sapphire results from a combination of titanium and iron oxides,