Which elements must be present in trace amounts for blue sapphires?

Which elements must be present in trace amounts for blue sapphires?

• A. Chromium and Vanadium
• B. Iron and Titanium
• C. Nickel and Cobalt
• D. Copper and Zinc

Answer: (B)

Blue color in sapphire comes from trace impurities in the crystal lattice of corundum. Specifically, small amounts of iron and titanium substitute into the aluminum sites in Al2O3, and their interaction creates the blue hue (often described as an intervalence charge transfer between Fe and Ti ions under light). This combination is the classic reason blue sapphires appear blue. Other elements like chromium produce red rubies, and while cobalt can color sapphires blue in some cases, the standard explanation for the blue variety is iron and titanium in trace amounts.

Blue color in sapphire comes from trace impurities in the crystal lattice of corundum. Specifically, small amounts of iron and titanium substitute into the aluminum sites in Al2O3, and their interaction creates the blue hue (often described as an intervalence charge transfer between Fe and Ti ions under light). This combination is the classic reason blue sapphires appear blue. Other elements like chromium produce red rubies, and while cobalt can color sapphires blue in some cases, the standard explanation for the blue variety is iron and titanium in trace amounts.