http://mineralsciences.si.edu/collections/newacquisitions.htm The National Gem and Mineral Collection is dynamic and growing, thanks in large part to many generous gifts of specimens and funds. The gems and minerals featured here are some of the more recent additions to the collection. Fri, 08 May 2009 18:16:39 GMT ListGarden Program 1.3.1 http://blogs.law.harvard.edu/tech/rss http://mineralsciences.si.edu/collections/newacquisitions/2009/opal09.htm Opals from Mezezo have been well-known for more than 10 years for their play-of-color chocolate opals. Other deposits discovered more recently from Welo yield precious white, fire, crystal and sometimes black opals. The opals you see here are a chocolate opal from Mezezo (8.86ct), and a crystal opal (33.15ct) and rough specimen (643.9ct) from Welo. Gem opal consists of tiny silica spheres tightly packed together; the voids or spaces between the spheres contain air or water. The play-of-color in opal is due to the orderly arrangement of these spheres acting like a diffraction grating, breaking visible white light in to separate colors. Opals are typically cut en cabochon or polished free-form to best show the play-of-colors. These beautiful Ethiopian opals are a wonderful addition and upgrade to the National Gem Collection and the first from Welo. Fri, 08 May 2009 18:16:34 GMT http://mineralsciences.si.edu/collections/newacquisitions/2009/grossular09.htm Tsavorite is a highly prized gem variety of grossular garnet. It was first discovered by Campbell Bridges in 1967 near Kenya’s Tsavo National Park. This region on the Kenya-Tanzania border remains the only source of gem tsavorite. The most valuable tsavorites are an intense green to blue-green and can sometimes be confused with emerald; a yellowish overtone is less desirable. This tsavorite is cut en cabochon. The inclusions in this gem appear to be corrosion tubes that were replaced with iron oxide, hence the rust colored tube-like inclusions. Tsavorite is a totally natural gemstone. It is not heated, oiled, filled, irradiated, or treated in any way. This variety of green garnet was named tsavorite in honor of Kenya’s Tsavo National Park, by Henry B. (Harry) Platt, former President of Tiffany & Co., and Campbell Bridges, President of Tsavorite USA. Fri, 08 May 2009 18:16:02 GMT http://mineralsciences.si.edu/collections/newacquisitions/2009/spessartine09.htm Spessartine is the manganese-rich member of the garnet family and is typically colored yellowish to reddish orange. Spessartine gems can be quite beautiful, but they are not commonly seen in jewelry because the supplies are limited. The major sources for gem quality spessartine are Sri Lanka and Brazil. Other important localities include Australia, Burma, India, Israel, Madagascar, Zambia, Nigeria, Namibia, and the United States. This is the first spessartine garnet from Madagascar in the National Gem Collection. Fri, 08 May 2009 18:15:24 GMT http://mineralsciences.si.edu/collections/newacquisitions/2009/orthoclase09.htm The minerals in the feldspar family make up more than half of the Earth's rocky crust. Occasionally these common minerals form crystals that shimmer like the light of the moon or a rainbow on a soap bubble. Called iridescence, this phenomenon is caused by light scattering, or diffracting, off closely spaced layers of different composition in the feldspar crystals. The gems cut from these iridescent crystals are called moonstone, sunstone, and labradorite. This 35.38 -carat moonstone is from Tanzania. Moonstones are prized for their beautiful blue iridescence, known as adularescence. Flawless, clear, or translucent gems exhibiting a rich blue sheen are most valuable. Moonstones are typically cut as cabochons to best show off the effect. The finest moonstone gems come from Sri Lanka, Burma, and India. This 35.38 carat gem is the first moonstone from Tanzania for the National Gem Collection. Fri, 08 May 2009 18:14:50 GMT