To determine whether or not turquoise is authentic, check for uniform color throughout the piece, opaqueness and low shine. Fake turquoise is often made from pale stones injected with dye, which appear overly shiny, clear and streaked, according to BJBead.com.
Another means of determining whether or not a stone is turquoise is to hold a hot pin to it. If the stone begins to melt or produces an artificial odor, it is likely plastic or covered in epoxy. In fact, a hot needle often penetrates the epoxy coating. Before purchasing purportedly turquoise pieces from jewelers and other sellers, check to see if they are reputable by researching them online. BJBead.com suggests asking for written documentation of the stone's authenticity before buying.
Turquoise Sky reports that fake turquoise pieces are often sold at lower prices than legitimate stones and cautions against buying turquoise at suspiciously steep discounts. These impostor stones are often made of epoxy and powdered turquoise placed around a rock base. Another trick used by fake turquoise producers is to cover a rock with dyed magnesite and howlite, which is known as buffalo turquoise. To find out for certain if a purchased piece is fake, send it to a professional lab for verification and ask for a written report.