the most common origin of color in a gemstone is a d-metal ion dopant . Thus ruby is metal containing around 0.2-1 atom per cent metal ion in place of the metal ion ,and its red color results from the absorption of green light in the visible spectrum as a result of the excitation of metal electron (section 20.4) The same ion is responsible for the green of emerald, the different colour reflects a different local coordination environment of the dopant. the host structure is beryl (beryllium aluminium silicate) and the metal ion is surrounded by six silicate ions, rather than the six metal ion in ruby ,producing absorption at the different energy. Other d-metal ions are responsible for the colour of other gemstones. Iron(II) produces the red of garnets and the yellow-green of peridots. Manganese(II) is responsible for pink color of some tourmaline.