How do gems likes rubies and red beryls get their red color? Learn the role impurity ions play in the coloration of these and other gemstones.
3 Minute Read
The resulting color from an impurity in a mineral depends on the following factors:
To explain this, I’ll use sapphire and ruby as my first gemstone examples. Chromium in corundum causes pink or red coloration.
Just aluminum (Al) and oxygen (O) comprise pure corundum. The chemical formula, Al2O3, gives their relative amounts. Pure corundum doesn’t absorb any light from the far ultraviolet to the mid-infrared range. Thus, it’s absolutely colorless.
Now, chromium is a metal. However, when a chromium atom takes part in making a chemical compound, it loses electrons and becomes an ion. In the case of chromium in aluminum oxide, it loses three electrons, so we say it’s trivalent. It has a valence of +3 (Cr3+).
The trivalent chromium impurity substitutes for the trivalent aluminum of corundum. The addition of the trivalent chromium colors a corundum…
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The resulting color from an impurity in a mineral depends on the following factors:
To explain this, I’ll use sapphire and ruby as my first gemstone examples. Chromium in corundum causes pink or red coloration.
Just aluminum (Al) and oxygen (O) comprise pure corundum. The chemical formula, AlO, gives their relative amounts. Pure corundum doesn’t absorb any light from the . Thus, it’s absolutely colorless.
Now, chromium is a metal. However, when a chromium atom takes part in making a chemical compound, it loses electrons and becomes an ion. In the case of chromium in aluminum oxide, it loses three electrons, so we say it’s trivalent. It has a valence of +3 (Cr3+).
The trivalent chromium impurity substitutes for the trivalent aluminum of corundum. The addition of the trivalent chromium colors a corundum…
How do gems likes rubies and red beryls get their red color? Learn the role impurity ions play in the coloration of these and other gemstones.
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