What metal impurity makes rubies red and emeralds green?
The background behind the colors of rubies and emeralds is the effect of metal impurities on their crystal structures. Rubies and emeralds are both gemstones, but their colors differ significantly. This is because they contain various metal impurities that affect their color.
The red color of rubies
The red color of rubies is due to the presence of chromium ions (Cr³⁺) in their crystal structure. Ruby is the red form of corundum (aluminum oxide, Al₂O₃), and when the corundum crystal contains small amounts of chromium ions, it gives ruby its characteristic red color. Chromium ions replace some of the aluminum ions in the corundum crystal structure, and this change causes light to be absorbed at certain wavelengths, which is visible to us as a red color.
The green color of emeralds
The green color of emeralds is due to the presence of chromium (Cr³⁺) and vanadium ions (V³⁺) in their crystal structure. Emerald is the green form of beryl (beryllium aluminum silicate, Be₃Al₂(SiO₃)₆). Chromium and vanadium ions replace part of the aluminum ions in the crystal structure of beryl, which causes light to be absorbed at certain wavelengths and appears to us as a green color. Although both rubies and emeralds contain chromium ions, their different crystal structures and other chemical factors cause them to appear different colors.
Summary
The red color of rubies is due to the presence of chromium ions (Cr³⁺) in the crystal structure of corundum, while the green color of emeralds is due to the presence of chromium (Cr³⁺) and vanadium ions (V³⁺) in the crystal structure of beryl. These metallic impurities affect the absorption and reflection of light, giving gemstones their characteristic colors.
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