• Question: Why are rubies red?

    Asked by carrieanne12 to Dave on 20 Jun 2013.
    • Photo: David Briggs

      David Briggs answered on 20 Jun 2013:

      Rubies are aluminium oxide crystals – which are a naturally pale blue. If you just have aluminium oxide, they are sapphires.

      However, if the crystals also contain tiny amounts of the element chromium, they turn red.

      So Rubies are red because they contain chromium.

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