Zemannite is a very rare
oxide mineral
The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the si ...
with the chemical formula Mg
0.5ZnFe
3+ 3">eO3sub>3·4.5H
2O. It crystallizes in the
hexagonal crystal system and forms small
prismatic
An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are ''not'' prisms. The most familiar type of optical ...
brown
crystals. 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, Sonora,
Mexico as an unnamed new mineral. It was not accepted then by the
International Mineralogical Association
Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...
(IMA) due to the uncertainty in its chemical composition.
[
The mineral structure was solved in 1967 by Eckhart Matzat as 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 (25 May 1923 – 16 October 2022) was an Austrian mineralogist and geologist.
Life and work
Zemann was born on 25 May 1923 in Vienna. He studied mineralogy at the University of Vienna where he received his PhD for work with Feli ...
(born 1923), who had worked extensively on tellurium minerals.[E. Matzat, SJ Wiliam]
''Zemannite, a new tellurite mineral from Moctezuma, Sonora, Mexico''
Canadian Mineralogist Vol. 10, 1969, pp. 139–140.
Later investigations showed that zemannite, as well as the related mineral kinichilite, often contains impurities of sodium and magnesium and thus the formula was refined to its current form, .
Related minerals
Zemannite is a secondary mineral produced by weathering of native
Native may refer to:
People
* Jus soli, citizenship by right of birth
* Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory
** Native Americans (disambiguation)
In arts and entert ...
tellurium minerals, such as sylvanite
Sylvanite or silver gold telluride, chemical formula , 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 c ...
or calaverite. As a result of this process, the elemental tellurium or tellurium- anions (Te2− or Te22−) transform into the Te4+ cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
bound with oxygen into the tellurate ion 3">eO3sup>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
270px, Shimoda City Hall
is a city and port located in Shizuoka Prefecture, Japan. , the city had an estimated population of 21,402 in 10,787 households, and a population density of 200 persons per km2. The total area of the city is . In the 1 ...
, Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
.
Morphology and structure
Zemannite crystallizes in the hexagonal crystal system, space group 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 3">eO3sup>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 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
An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are ''not'' prisms. The most familiar type of optical ...
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.[
]
References
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,
External links
Spectroscopic data for Zemannite
{{Selenites, selenates, tellurites, and tellurates
Oxide minerals
Iron(III) minerals
Magnesium minerals
Tellurite and selenite minerals
Hexagonal minerals
Minerals in space group 176