Abstract The coloration mechanism of gemstones is discussed by chemical composition and absorption spectrum. The colorations of ruby, sapphire, and emerald result from the d-d electron transition and charge transfer transition of transition metal ions such as chromium, iron, titanium etc. The colorations of ruby and sapphire are not simply dependent on the content of chromium or/and iron, but more dependent
on the ratio of Fe2+/Ti4+and Fe3+/Fe2+. The coloration of emerald results from the effect of transition metal ions such as iron, chromium and vanadium etc. The coloration of gemstones may also relates to other transition metal ions and color centers, which may contribute more beautiful color.