Sewardite
Encyclopedia
Sewardite is a rare arsenate mineral
with formula of CaFe2+3(AsO4)2(OH)2. Sewardite was discovered in 1982 and named for the mineralogist, Terry M. Seward (1940-), a professor of geochemistry
in Zürich
, Switzerland
.
In terms of its optical properties, sewardite is weak anisotropic, which means the velocity of light varies depending on the direction through the mineral. Its color in plane-polarized light is dark red, and it does not exhibit pleochroism, which means it does not appear to be a different color when observed at different angles under a polarizing petrographic microscope. Sewardite illustrates weak birefringence; birefringence is directly dependent on the material being anistropic, so since sewardite is weakly anistropic, it exhibits weak birefringence.
, Namibia
, Mina Ojuela, Mapimi, Durango
, Mexico
, and La Mur, Las Animas mine, Sonora
, Mexico. The Tsumeb Mine is the most prolific mine in the world, and occurs in a geologic setting of the subduction belt of Namibia, which produces the conditions in which sewardite occurs. At the site in Durango, Mexico, it occurs as a dark, reddish spherules and rosettes of very thin, flaky crystals that would be compacted together in sparkling masses.
This newly discovered mineral (confirmed as a species in 1998) has been determined as rare, since only 1-2 mg of it have been found on Earth. Since it's such a rarity, any use found for the mineral would be very impractical due to its existing quantity.
Arsenate mineral
Arsenate minerals usually refer to the naturally occurring orthoarsenates, possessing the 3- anion group and, more rarely, other arsenates with anions like AsO32- or [AsO22]- . Arsenite minerals are much less common...
with formula of CaFe2+3(AsO4)2(OH)2. Sewardite was discovered in 1982 and named for the mineralogist, Terry M. Seward (1940-), a professor of geochemistry
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
in Zürich
Zürich
Zurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
.
Properties
Sewardite is orthorhombic, which means in crystallographic terms, it contains 3 axes of unequal length, one "c" axis, and 1 "a" axis, and 1 "b" axis. The "c" axis runs vertically, and the "b" axis forms a 90 degree angle with the "c" axis; the "a" axis forms an angle that is less than 90 degrees. It's class structure in the crystal system, orthorhombic, is mmm (2/m 2/m 2/m) - dipyramidal. Sewardite can form platy to compact anhedral to subhedral masses up to 0.3 mm in size in a single specimen.In terms of its optical properties, sewardite is weak anisotropic, which means the velocity of light varies depending on the direction through the mineral. Its color in plane-polarized light is dark red, and it does not exhibit pleochroism, which means it does not appear to be a different color when observed at different angles under a polarizing petrographic microscope. Sewardite illustrates weak birefringence; birefringence is directly dependent on the material being anistropic, so since sewardite is weakly anistropic, it exhibits weak birefringence.
Occurrence
Sewardite has only been found at three locations, in the Tsumeb mine in TsumebTsumeb
Tsumeb is a city of 15,000 inhabitants and the largest town in Oshikoto region in northern Namibia. Tsumeb is the home of the world-famous Tsumeb mine, and the "gateway to the north" of Namibia. It is the closest town to the Etosha National Park...
, Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
, Mina Ojuela, Mapimi, Durango
Durango
Durango officially Estado Libre y Soberano de Durango is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. The state is located in Northwest Mexico. With a population of 1,632,934, it has Mexico's second-lowest population density, after Baja...
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, and La Mur, Las Animas mine, Sonora
Sonora
Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo....
, Mexico. The Tsumeb Mine is the most prolific mine in the world, and occurs in a geologic setting of the subduction belt of Namibia, which produces the conditions in which sewardite occurs. At the site in Durango, Mexico, it occurs as a dark, reddish spherules and rosettes of very thin, flaky crystals that would be compacted together in sparkling masses.
This newly discovered mineral (confirmed as a species in 1998) has been determined as rare, since only 1-2 mg of it have been found on Earth. Since it's such a rarity, any use found for the mineral would be very impractical due to its existing quantity.