Sapphire
Sapphires are blue, rubies are red. Everyone knows that. Except that it's not quite true.
Sapphire and ruby are both types of corundum, a form of aluminium oxide. Early societies believed them to be distinct stones hence they have different names. However the only real difference is the colour. Red corundum is defined as ruby, all other colours are sapphire.
So although blue sapphire remains the most well known form, you can buy it in just about any colour except red. There are even colour changing forms of sapphire that vary their hue according to the type of light. As with other stones, natural sapphires with a pale hue are sometimes treated to enhance and lock in the colour.
Despite this, sapphires continue to be associated with the colour blue leading to terms such as "sapphire seas".
As with most gemstones it's possible to buy both natural and lab-created sapphires. It can be difficult for a layman to tell the difference.
Pink Sapphires
So if red corundum is ruby and all other colours are sapphire, what about pink? Or dark pink? Or light red?In earlier centuries the pink stones were considered light rubies (sometimes referred to as "female"). At some time around the start of the twentieth century people started to distinguish between "pink" and "light red" as separate colours. This is probably where the confusion began and for many years the decision whether to classify pink corundum as ruby or sapphire used to be pretty much a matter of taste.
The wheel now appears to have turned full circle and the International Colored Gemstone Association has now decided that for simplicity all pale red corundum should be classified as ruby. However many people still keep the old names and you can still buy pink sapphire rings, bracelets and other jewelry.