Sapphires and Rubies     If the diamond is the ruler of the gemstones, then the sapphires and rubies are the crown princes.  Chemically, these gemstones are aluminum oxide in a beautiful crystalline form.  Actually they are brothers, both constituting the mineral corundum.  They differ only in the trace elements that they contain.  These trace elements are called chromophores and give them their distinctive colors.

Sapphires come in many colors, from cornflower blue to black, but the blue color is most often associated with the sapphire.  When the trace element is chromium, the color is red and gemstone is called a ruby.  The most highly prized is the pigeon-blood red, that is, a red with a purplish tinge.

Sapphires and rubies are next to diamonds in hardness, being 9 on the Mohs' scale.  This scale is not really linear; the diamond is much harder by comparison.

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