Apart from diamonds, rubies and sapphires are perhaps the most important gemstones. The price of high quality rubies and sapphires when it comes from a certain region may perhaps be more than high quality diamonds on a per carat basis.
Rubies and sapphires belong to the same family species called Corundum but are called by their variety name.
Corundum also comes in all hues of colors too. You have the colorless corundum, yellow, green, orange, purple and all colors of the rainbow. Under the classification of varieties ruby is red, sapphire is blue, colorless sapphire and all other types of color are called by their name of Fancy Sapphire or their color variety, like Yellow Sapphire.
The chemical composition of corundum is Aluminum Oxide, or Al2O3. In its pure state it is colorless. During its crystallization process, impurities from the surrounding environment may find its way into the molecular structure of the crystal. Impurities of trace element then give rise to certain color varieties.
The trace element of Chromium ( Cr3+ ) gives the gems a red color and we called it a ruby. Sapphire is caused by the trace elements of Ferrous Oxide ( Fe2+ ) and Titanium ( Ti4+ ). Other trace elements will give rise to a mix of colors.
Now these are all the basics of corundum.
It is important that one learn the fundamentals and once you understand the fundamentals you will be able to grasp some more complex issues of gemstones identification, how gems are being enhanced to give it a more vivid color or to alter the color of a gemstone by using a combination of trace elements by heating it to almost its melting point.
Look out for more posts on rubies and sapphires stage by stage.