Howlite and magnesite can easily be separated from turquoise using a refractometer. They have different refractive indexes. If you are willing to do a destructive test, the blue dye used to color howlite and magnesite generally does not penetrate very deep. If lightly dyed, scratching the back of a cabochon with a pin will often reveal a white interior. If the piece is heavily dyed, scratching deeper or breaking an edge might be required to determine if the piece has been dyed.

Several minerals are found where turquoise is expected, look similar to turquoise, are misidentified as turquoise, and often enter the gem and jewelry market labeled as turquoise. Variscite, chalcosiderite, and magnesite are examples. A yellow, white, brown or green color should be an immediate clue that these might not be turquoise. An easy-to-do refractive index test will quickly separate all of these minerals from turquoise. Turquoise has a refractive index of 1.61 to 1.65. All of these other minerals are different as shown in the accompanying table.