Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet and green are the most common secondary hues found in blue sapphires.Blue sapphires with any amount of green as a secondary hue are not considered to be of fine quality.
Here's some facts/trivia about sapphires:
*So strong is the power of a sapphire, it has been said that a venomous snake put in a vessel made of sapphire would quickly die. Sapphires therefore earned the reputation as an excellent all-purpose medicine and were ingested as an antidote to poison
* Sapphire is the birthstone for September and the gemstone given for anniversaries of the 5th and 45th years
*Sapphires are favored in the western world because their coloring is so sympathetic to the complexions of northern women. Just think of Princess Diana and her HUGE sapphire engagement ring
*In the Middle and Far East a sapphire is thought to be either extremely lucky or unlucky. Inconveniently, it is not until you wear it that you know which!
*The 423 carats (85g) Logan sapphire in the National Museum of Natural History in Washington DC is one of the largest faceted gem-quality blue sapphires in existence. Ooooh! Wouldn't you like to get your hands on that beauty?