Turquoise is a hydrous copper alumino-phosphate. Its formula is CuAl6(PO4)4(OH)8 · 4H2O
It is estimated that between 75-90% of commercially available turquoise on the market today has been treated or stabilized in some fashion. Most commonly, epoxy/resin is injected into less competent turquoise material to strengthen it. Some commercial turquoise products may contain significant amounts of planerite, a similar mineral that contains no copper.
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