The hot gem varieties such as Ruby, Emerald, Alexandrite, Tsavorite, Demantoid, and Spinel in the jewelry market are bright, gaudy and showy, which satisfy our superior visual enjoyment. All of this is inseparable from a mysterious and mysterious element, chromium.
In 1797, a French chemist discovered the chromium for the first time in chrome lead ore. The elementary substance of chromium is steel gray, which is the hardest metal. The element name of chromium comes from Greek, which means "color" since the chromium compounds have color, such as metal chromium is silvery white sparkling, chromium sulfate is green, chromic acid magnesium is yellow, potassium dichromate is orange, chromate is scarlet, chrome oxide is green, chrome alum is of blue-purple, lead chromate is yellow...
In many colored gemstones, the chromium ion can partially replace other metal ions in similar valence states, which will form the isomorphous substitution to produce different colors.
When the Al ions in Al2O3 are replaced by the chromium part, the corundum, which should be pure and colorless, will turn red. Moreover, the depth of the red color changes with the content of chromium. When the Al ions in the emerald (Be3Al2Si6O18) are replaced by the chromium part, the emerald will show bright green again. This is because the chromium is a transition metal element. The sub outer d orbital of this type of element is connected to the outermost s orbital, and the d orbital has not yet reached a stable structure, so both the s and the d electrons can participate in some or all of the bonding. Therefore, when Cr ions are in different gemstone varieties, the crystal field environment and the effect intensity is different, which leads to different light waves absorbed by electronic transitions, and the color of the gemstones varies.