|
|
|
| Current Issue |
|
|
| Resources |
|
|
|
Cerussite
| Article
# : |
13015 |
|
|
Section : |
NATURAL SCIENCE
|
| Issue
Date : |
5 / 1987 |
744 Words |
| Author
: |
Paul E. Desautels
Paul E. Desautels is a former curator of gems and minerals at
the Smithsonian Institution, Washington, D.C., and is
currently a consultant to the Houston Museum of Natural
Science. |
When natural beauty is a topic of discussion, the easily accessible beauty of birds and flowers, clouds and sunsets, trees and forests, and mountains, rivers and lakes tends to come to mind. But few people have direct contact with mineral specimens of high aesthetic appeal and hence are not aware of their intrinsic beauty. Minerals can be breathtakingly beautiful. The color and form of a species can result in a durable object able to hold its own with the finest sculptures. As frequently attested by prices they will pay, connoisseurs among mineral specimen collectors have long recognized this fact.
One such species, highly coveted by collectors, is known as cerussite (ser-oos-ite). Because of its chemical composition - cerussite is a simple lead carbonate - it should never be colored. But sometimes small impurities in the deposit impart a hint of color to individual specimens. The material was recognized in antiquity, as early as 400 B.C., and Pliny, the great Roman natural historian, knew of it as cerussa. Thus, the origin of our modern name for the species is obvious.
Although not nearly as plentiful as galena, which is the common ore of lead, cerussite occurs and has been mined in many lead deposits around the world. It has been described in mineralogical literature from places as exotic as Johanngeorgenstadt in Saxony; Mknteponi in Sardinia; Andalusia in Spain; Leadhills, Lanarkshire, in Scotland; Sidi-Amor-ben-Salem in Tunisia; Broken Hill in New South Wales, Australia; and the Mammoth Mine at Tiger, Arizona.
The most extraordinary cerussite specimens have come in recent years from the important copper mines at Tsumeb in Namibia. It may seem a bit odd for superb lead-mineral specimens to be found in a copper mine. However, geologists learn early in their careers that copper, lead, and zinc minerals are frequently found together in deposits because of certain similarities in their chemistries. One of the things that makes some Tsumeb cerussite specimens so desirable to collectors is their frequent occurrence in the same deposits with other beautifully formed and highly colored species. These include bright blue azurite (a copper carbonate), rich green malachite (another kind of copper carbonate), pink or green smithsonite (zinc carbonate) and yellow mimetite (lead chlor arsenate).
Secondly, all of these species at Tsumeb, including the cerussite, have had the appropriate conditions of temperature, pressure, time, space, concentration of solutions, long-time stability of the deposit, and so forth, to form crystals. All
...
Read Full Article
Look for this article in Ask.com
|
|
