How to Choose High-Quality Turquoise. Often thought of as a product of the American Southwest, turquoise is also mined in Mexico, China, Iran, Tibet and Australia. One of the most familiar minerals, turquoise is said to promote prosperity, protect from evil, keep one from falling off a horse and guide arrows to hit their marks.
Deal with reputable merchants; avoid purchasing turquoise from sources that are unknown to you.
Always ask if the stone has been treated in any way - this can be a clue if it's an imitation. (Expect it to have some kind of coating, which is often done.)
Look at the color of the stone. The most valuable turquoise is clear blue without any greenish cast or veins in it. However, some people prefer turquoise with veins in it for the contrast it provides to the color of the stone.
Check the condition of the stone. It shouldn't have any chips or fractures.
Compare several pieces of turquoise side by side. Look at the color and texture, and select the piece you like best.