Turquoise
Turquoise, chemically, is a hydrated phosphate of copper and aluminum and is formed by the percolation of meteoric or groundwater through aluminous rock in the presence of copper. For this reason, it is often associated with copper deposits as a secondary mineral. Turquoise is most often found in arid, semiarid or desert places such as Iran, Tibet, China, Australia, Mexico, Russia, Turkestan and the southwest U.S.
Turquoise gets its color from the heavy metals in the ground where it forms. Blue turquoise forms when there is copper present, which is the case with most Arizona turquoise. Green turquoise forms where iron is present, the case with most Nevada turquoise. Matrix is the host rock, mother rock. It can be made from several different elements such as pyrite, chert, quartz, cuperite and manganese oxide. The sought after spider web turquoise is made up of small nuggets naturally cemented together with rock or matrix. When cut and polished the stone resembles a spider web.
So many geologic chains of events must synchronize to create just one thin vein of turquoise that the mineral can rightly be envisioned as a fluke of nature. Turquoise is the rare and improbable product of an incalculable number of chemical and physical processes that must take place in the right combination and proper environment over a time span of hundreds of thousands – if not millions – of years. |
Silver
The word "sterling" has been used to mean high-quality
silver since the 1200's. At that time, the coins of England had decreased
in value and contained only a little silver.The only European coins
that contained large proportions of silver, were those made by the
merchants of the Hanseatic League, a group of trading cities in Northern
Germany.These coins were called "Easterlings" to distinguish
them from the low-silver alloy coins of England. English speech
contracted "Easterling" to "Sterling". |
