Turquoise, CuAl_6 (PO_4)_4 (OH)_8 5H_2O, is hydrated copper aluminum phosphate.

Question

Turquoise, CuAl_6 (PO_4)_4 (OH)_8 5H_2O, is hydrated copper aluminum phosphate. It is a valuable mineral and is perhaps the most valuable nontransparent mineral in the jewelry trade. The color of turquoise varies between pale green and turquoise, which is where the color got its name. Why would turquoise commonly change colors when exposed to skin oils from normal jewelry wear? Based upon your recent experiments, what might an unscrupulous mineral trader treat (soak) a low-grade pale-green turquoise with to cause it to change into much more valuable turquoise color? (This is technically illegal.)

Explanation / Answer

a) Turquoise is a porous stone which is hydrated phosphate of copper and aluminum (CuAl6(PO4)4(OH)8·5H2O). When exposed to skin oils, small amounts of iron substitute aluminum in the turquoise structure which imparts green colour in proportion to its abundance in the stone.

b) Which experiment ??? Turquoise can be treated in a number of ways.

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