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Why don’t the different colors of Corundum reflect the chemicals in their formula?

–1 vote
Shouldn’t it be

Corundum - Al2O3

Sapphire - Al2O3(Fe,Ti) Blue

Sapphire - Al2O3(V) - Violet


I am no chemist but it just seems that it would make sense to attribute what gives them the color as it is also part of the make up.

Thanks for your time!
asked Nov 16, 2017 by JamesLeader (110 points)

1 Answer

0 votes

Because crystals are not always pure and the inclusions of trace elements is what causes the color, it would seem natural to include a reference to the trace elements, however, for expedience, corundum is corundun whether it is ruby or sapphire and is not essential to the chemical formula. Your milk is just milk, or is it? There are trace elements in milk, we don't list them. Same here. Sapphire is Al2O3 and iron and Titanium causes the color but to list all the trace elements in sapphire would be tedious and different for every sapphire. I hope that helps.

answered Nov 23, 2017 by Weasel (58,980 points)
Weasel is correct. The volume of the impurities that cause these colors are just too weak to include them within the formula, even a variable formula.

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