geo11 - Madison 6:18 PM Lecture 11 Soft gems CopperBearing...

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2/5/09 6:18 PM :. Madison .: Page 1 of 8 Lecture 11: Soft gems: Copper- Bearing gemstones, rhodochrosite, and others I. Low-Temperature Copper-bearing minerals Nearly all of the following minerals form at low temperature and pressure, often very close to the surface of the earth. All require water either in the form of rain ( sometimes called meteoric ) or ground water. The copper is in solution within the water, and as the water evaporates, it reacts with other minerals, creating vividly hued copper - bearing minerals. Arid regions where evaporation is high, often have the largest deposits of these minerals. Turquoise Turquoise commonly occurs in veinlets penetrating weathered, aluminum - rich, sedimentary or volcanic rocks ( where it has been deposited near the surface from circulating phosphatic waters ) in arid climates, and in small, fine - grained, rounded masses and crusts. Turquoise cabochons set in a silver Navajo bracelet. Turquoise is a "cryptocrystalline" material you will rarely see individual crystals. It is a hydrous (water) Cu- bearing phosphate mineral. Turquoise is formed in association with Cu-rich deposits; copper is transported in waters which interact with phosphorous and aluminum-bearing rocks. Turquoise is often veined and frequently contains inclusions of surrounding rocks it occurs as kidney-shaped (reniform) or grape-like aggregates. · Hardness= 5 - 6
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2/5/09 6:18 PM :. Madison .: Page 2 of 8 · Color: medium green-blue (greener material contains more Fe) · greasy (waxy) luster · Chemical formula: CuAl6(PO4)4(OH)8 5H2O Well known deposits occur in Persia, Sinai Peninsula, China, Chile, Egypt, Turkey, Mesoamerica ( Arizona ) . Turquoise is sometimes referred to as "Turkish stone," which might account for the origin of its name. Turquoise's use dates back to 3000 B.C. - 4000 B.C.+ ( Sinai ) . Turquoise is sensitive to temperatures above 250 degrees C. This will evaporate the water in the crystal structure - a loss of water leads to a dull green color. Turquoise is sometimes impregnated with plastic, parafin, oil, or dyed to improve
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This note was uploaded on 02/11/2009 for the course GEO 331 taught by Professor Huifang during the Spring '07 term at University of Wisconsin.

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geo11 - Madison 6:18 PM Lecture 11 Soft gems CopperBearing...

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