Discovered in the late 1960s in Tanzania, and found exclusively in this tiny area of the world, tanzanite exhibits a rich violet-blue colour for which the gemstone is treasured; often it is heat-treated to achieve this colour. Colours range from blue to purple, and tanzanites that are medium dark in tone, vivid in saturation, and slightly violet blue command premium prices. As tanzanite can be less expensive than sapphire, it often was purchased as an alternative. However, it has increased in popularity and now is valued more for its own beauty and brilliance than as a sapphire substitute.
Derived from the Arabic words zar and gun, meaning gold and colour, zircon is found in a wide range of colours such as: blue, yellow, orange, brown, green, colourless, and red (the most prized colour). For many years colourless zircon was used to imitate diamonds. Folk wisdom grants zircon the power to relieve pain, whet the appetite, protect travellers from disease and injury, to ensure a warm welcome, and to prevent nightmares guaranteeing a deep, tranquil sleep. Major sources of zircon are the Chanthaburi area of Thailand, the Palin area of Cambodia, and the southern part of Vietnam.
The name turquoise, from the French expression Pierre tourques or Turkish stone, originated in the thirteenth century and describes one of the oldest known gemstones. Turquoise varies in colour from greenish blue, through robin’s egg-blue, to sky blue shades and its transparency ranges from translucent to opaque. Turquoise is plentiful and is available in a wide range of sizes. It is most often used for beads, cabochons, carvings, and inlays. Although its popularity fluctuates in fashion, it is a perennial favorite in the American Southwest.
Information from http://www.americangemsociety.org