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How to buy turquoise jewelry 
Learn the difference between real turquoise and imitation turquoise. 
Natural turquoise, an aggregate of copper aluminum phosphate hydrate, formed under heat and pressure, is often soft or porous when mined. The various colors found in turquoise result from the presence of either copper or iron--vivid blue is from copper and the softer green tones from iron.
Turquoise stones can also have patterns of brown, yellow ochre and black matrix, produced from copper compounds. True turquoise has an opaque, waxy luster that may or may not include matrix, depending on the type of turquoise.