Zemannite
Encyclopedia
Zemannite is a very rare oxide mineral
with the chemical formula Mg0.5ZnFe3+[TeO3]3·4.5H2O. It crystallizes in the hexagonal crystal system
and forms small prismatic
brown crystal
s. Because of the rarity and small crystal size, zemannite has no applications and serves as a collector's item.
, Mexico
as an unnamed new mineral. It was not accepted then by the International Mineralogical Association
(IMA) due to the uncertainty in its chemical composition.
The mineral structure was solved in 1967 by Eckhart Matzat as (Na,H)2(Zn,Fe)3+(Mn,Mg)2[TeO3]3·nH2O is specified. Two years later, the mineral was recognized by the IMA under the name zemannite, in honor of the Austrian mineralogist Josef Zemann
(born 1923), who had worked extensively on tellurium minerals.
Later investigations showed that zemannite, as well as the related mineral kinichilit, often contains impurities of sodium
and magnesium
and thus the formula was refined to its current form, Mg0.5ZnFe3+[TeO3]3·4.5H2O.
of native
tellurium minerals, such as sylvanite
or calaverite
. As a result of this process, the elemental tellurium or tellurium-anions (Te2− or Te22−) transform into the Te4+ cation bound with oxygen into the tellurate
ion [TeO3]2−.
Zemannite is chemically and structurally similar to keystoneite and kinichilite; together, these minerals form the so-called "zemannite group".
In addition to Moctezuma, zemannite was also found in Vielsalm
– a municipality
in the Belgian
province of Luxembourg and near Shimoda, Shizuoka
, Japan
.
P63m with the lattice parameters a = 941 pm and c = 764 pm and two formula units per unit cell. The Te4+ bind with three oxygen atoms forming [TeO3]2− anions, where oxygens form trigonal pyramids around the tellurium ion. The Zn2+ and Fe3+ cations share the same cite with typical respective probabilities of 40% and 60%; those values can vary from crystal to crystal. The Mn2+ impurity, if present, also shares the same site. This site is surrounded by a distorted octahedron
of six oxygen atoms. These tellurium-oxygen and Fe/Zn-oxygen polyhedra form a network with wide (0.83 nm diameter) channels parallel to the crystallographic c axis (normal to the picture). Therefore, zemannites are often attributed to zeolite
materials. The channels are often occupied by sodium impurity and water.
The Mg2+ cations form octahedral Mg[(H2O)6]2+ complexes with six water molecules which are located in the channels of the crystal structure. The occupancy of the Mg sites is 50% which is reflected by the coefficient 0.5 in the chemical formula.
Zemannite forms prismatic
crystals, usually smaller than 1 mm. Because zemannite is secondary mineral, its crystals usually on other rocks and retain the hexagonal shape corresponding to their crystal symmetry. The ideal pyramidal tips, as in the infobox image, are often absent.
Oxide mineral
The oxide mineral class includes those minerals in which the oxide anion is bonded to one or more metal ions. The hydroxide bearing minerals are typically included in the oxide class...
with the chemical formula Mg0.5ZnFe3+[TeO3]3·4.5H2O. It crystallizes in the hexagonal crystal system
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
and forms small prismatic
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
brown crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s. Because of the rarity and small crystal size, zemannite has no applications and serves as a collector's item.
History and etymology
Zemannite was discovered in 1961 in a tellurium deposit near Moctezuma, SonoraMoctezuma, Sonora
Moctezuma is a municipio of the Mexican state of Sonora, located in the state's central region. It is also the name of its largest settlement and cabecera municipal .-Area and Population:...
, 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...
as an unnamed new mineral. It was not accepted then by the International Mineralogical Association
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
(IMA) due to the uncertainty in its chemical composition.
The mineral structure was solved in 1967 by Eckhart Matzat as (Na,H)2(Zn,Fe)3+(Mn,Mg)2[TeO3]3·nH2O is specified. Two years later, the mineral was recognized by the IMA under the name zemannite, in honor of the Austrian mineralogist Josef Zemann
Josef Zemann
-Life and work:Zemann was born in 1923 in Vienna and studies mineralogy at the University of Vienna were he received his PhD for work with Felix Machatschki in 1946. Zemann worked with Martin J. Buerger at the Massachusetts Institute of Technology in 1951 and 1952. He became director of the...
(born 1923), who had worked extensively on tellurium minerals.
Later investigations showed that zemannite, as well as the related mineral kinichilit, often contains impurities of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
and thus the formula was refined to its current form, Mg0.5ZnFe3+[TeO3]3·4.5H2O.
Related minerals
Zemannite is a secondary mineral produced by weatheringWeathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
of native
Native Metal
A native metal is any metal that is found in its metallic form, either pure or as an alloy, in nature. Metals that can be found as native deposits singly and/or in alloys include aluminium, antimony, arsenic, bismuth, cadmium, chromium, cobalt, indium, iron, nickel, selenium, tantalum, tellurium,...
tellurium minerals, such as sylvanite
Sylvanite
Sylvanite or silver gold telluride, Te2, is the most common telluride of gold.-Properties:The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with...
or calaverite
Calaverite
Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...
. As a result of this process, the elemental tellurium or tellurium-anions (Te2− or Te22−) transform into the Te4+ cation bound with oxygen into the tellurate
Tellurate
The tellurate ion is TeO42− or TeO66−.Unlike sulfate, tellurate is a somewhat good oxidizer; it can be reduced to tellurite or tellurium....
ion [TeO3]2−.
Zemannite is chemically and structurally similar to keystoneite and kinichilite; together, these minerals form the so-called "zemannite group".
In addition to Moctezuma, zemannite was also found in Vielsalm
Vielsalm
Vielsalm is a Walloon municipality of Belgium located in the province of Luxembourg.On 1 January 2007 the municipality had 7,339 inhabitants...
– a municipality
Municipality
A municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...
in the Belgian
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
province of Luxembourg and near Shimoda, Shizuoka
Shimoda, Shizuoka
is a city and port in Shizuoka, Japan.As of 2010, the city had an estimated population of 25,054 and a population density of 242 persons per square kilometer...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
.
Morphology and structure
Zemannite crystallizes in the hexagonal crystal system, space groupSpace group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
P63m with the lattice parameters a = 941 pm and c = 764 pm and two formula units per unit cell. The Te4+ bind with three oxygen atoms forming [TeO3]2− anions, where oxygens form trigonal pyramids around the tellurium ion. The Zn2+ and Fe3+ cations share the same cite with typical respective probabilities of 40% and 60%; those values can vary from crystal to crystal. The Mn2+ impurity, if present, also shares the same site. This site is surrounded by a distorted octahedron
Octahedron
In geometry, an octahedron is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex....
of six oxygen atoms. These tellurium-oxygen and Fe/Zn-oxygen polyhedra form a network with wide (0.83 nm diameter) channels parallel to the crystallographic c axis (normal to the picture). Therefore, zemannites are often attributed to zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
materials. The channels are often occupied by sodium impurity and water.
The Mg2+ cations form octahedral Mg[(H2O)6]2+ complexes with six water molecules which are located in the channels of the crystal structure. The occupancy of the Mg sites is 50% which is reflected by the coefficient 0.5 in the chemical formula.
Zemannite forms prismatic
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
crystals, usually smaller than 1 mm. Because zemannite is secondary mineral, its crystals usually on other rocks and retain the hexagonal shape corresponding to their crystal symmetry. The ideal pyramidal tips, as in the infobox image, are often absent.
Further reading
- RV Gaines:The Moctezuma tellurium Deposit. In:Mineralogical Record. No. 1, 1970, pp. 40–43.
- S. White:The big Lapis minerals directory. 4th Edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6