Khatyrkite ( ) is a rare mineral which is mostly composed of
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
and
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, but may contain up to about 15% of
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
or
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
.
Its chemical structure is described by an approximate formula or . It was discovered in 1985 in a placer in association with another rare mineral cupalite (). These two minerals have only been found at in the area of the Iomrautvaam, a tributary of the Khatyrka river, in the Koryak Mountains
The Koryak Mountains or Koryak Highlands () are an area of mountain ranges in Far-Eastern Siberia, Russia, located in Chukotka Autonomous Okrug and in Kamchatka Krai, with a small part in Magadan Oblast. The highest point in the system is the ...
, in Anadyrsky District (former Beringovsky District), Chukotka, Russia
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
. Analysis of one of the samples containing khatyrkite showed that the small rock was from a meteorite. A geological expedition has identified the exact place of the original discovery and found more specimens of the Khatyrka meteorite. The mineral's name derives from the Khatyrka (russian: Хатырка) zone where it was discovered. Its type specimen
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...
(defining sample) is preserved in the Mining Museum in Saint Petersburg
Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
, and parts of it can be found in other museums, such as Museo di Storia Naturale di Firenze
The Museo di Storia Naturale di Firenze is a natural history museum in 6 major collections, located in Florence, Italy. It is part of the University of Florence. Museum collections are open mornings except Wednesday, and all day Saturday; an adm ...
.[
]
Properties
In the initial studies of khatyrkite, a negative correlation was observed between copper and zinc, i.e. the higher the copper the lower the zinc content and vice versa, which is why the formula was specified as . It was found later that iron can be substituted for zinc.[ The mineral is opaque and has a steel-gray yellow tint in reflected light, similar to native ]platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Pla ...
. Isotropic sections are light blue whereas anisotropic ones are blue to creamy pink. Strong optical anisotropy is observed when the crystals are viewed in polarized light. Khatyrkite forms dendritic, rounded or irregular grains, typically below 0.5 millimeter in size, which are intergrown with cupalite. They have a tetragonal
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...
symmetry with point group 4/m 2/m 2/m, space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...
I4/mcm and lattice constants ''a'' = 0.607(1) nm, ''c'' = 0.489(1) nm and four formula unit
In chemistry, a formula unit is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. E ...
s per unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
. The crystalline structure parameters are the same for khatyrkite and synthetic CuAl2 alloy. The density, as calculated from XRD the lattice parameters, is 4.42 g/cm3. The crystals are malleable
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, that is they deform rather than break apart upon a strike; they have the Mohs hardness
The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.
The scale was introduced in 1812 by t ...
is between 5 and 6 and Vickers hardness
The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness t ...
is in the range 511–568 kg/mm2 for a 20–50 gram load and 433–474 kg/mm2 for a 100 gram load.[
Khatyrkite and cupalite are accompanied by spinel, corundum, stishovite, augite, forsteritic ]olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
, diopsidic clinopyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...
and several Al-Cu-Fe metal alloy minerals. The presence of unoxidized aluminium in khatyrkite and association with the stishovite—a form of quartz which exclusively forms at high pressures of several tens gigapascals—suggest that the mineral was formed in a high-energy impact involving the object that became the Khatyrka meteorite.
*
Relation to quasicrystals
Khatyrkite is remarkable in that it contains micrometre-sized grains of icosahedrite
Icosahedrite is the first known naturally occurring quasicrystal phase. It has the composition Al63Cu24Fe13 and is a mineral approved by the International Mineralogical Association in 2010. Its discovery followed a 10-year-long systematic search ...
, the first known naturally occurring quasicrystal
A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical ...
—aperiodic and yet ordered in structure. The quasicrystal has a composition of Al63Cu24Fe13 which is close to that of a well-characterized synthetic Al-Cu-Fe material.[ It is thought that the icosahedrite, like the khatyrkite, was formed in space in a collision involving the parent body of the meteorite.][
A second natural quasicrystal, called decagonite, Al71Ni24Fe5 with a ]decagon
In geometry, a decagon (from the Greek δέκα ''déka'' and γωνία ''gonía,'' "ten angles") is a ten-sided polygon or 10-gon.. The total sum of the interior angles of a simple decagon is 1440°.
A self-intersecting ''regular decagon'' i ...
al structure has been identified by Luca Bindi
Luca Bindi (born 1971) is an Italian geologist. He holds the Chair of Mineralogy and Crystallography and is the Head of the Department of Earth Sciences of the University of Florence. He is also a research associate at the Istituto di Geoscienze e ...
in the samples and announced in 2015. Another variant was announced the following year.[Bindi L., Chaney Lin, Chi Ma & Paul J. Steinhardt, ''Collisions in outer space produced an icosahedral phase in the Khatyrka meteorite never observed previously in the laboratory'']
Nature - Scientific reports
Dec. 2016
Quasicrystals were first reported in 1984 and named so by Dov Levine and Paul Steinhardt
Paul Joseph Steinhardt (born December 25, 1952) is an American theoretical physicist whose principal research is in cosmology and condensed matter physics. He is currently the Albert Einstein Professor in Science at Princeton University, where ...
.[Exotic Quasicrystal May Represent New Type of Mineral]
Scientific American, 4 June 2009 More than 100 quasicrystal compositions have been discovered by 2009—all synthesized in the laboratory. Steinhardt initiated a large-scale search for natural quasicrystals around the year of 2000 using the database of the International Centre for Diffraction Data
The International Centre for Diffraction Data (ICDD) maintains a database of powder diffraction patterns, the Powder Diffraction File (PDF), including the d-spacings (related to angle of diffraction) and relative intensities of observable diffrac ...
. About 50 candidates were selected out of 9,000 minerals based on a set of parameters defined by the structure of the known quasicrystals. The corresponding samples were examined with X-ray diffraction and transmission electron microscopy
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a g ...
but no quasicrystals were found. Widening of the search eventually included khatyrkite. A sample of the mineral was provided by Luca Bindi of the Museo di Firenze and was later proven to be part of the Russian holotype specimen. Mapping its chemical composition and crystalline structure revealed agglomerate of grains up to 0.1 millimeter in size of various phases, mostly khatyrkite, cupalite (zinc or iron containing), some yet unidentified Al-Cu-Fe minerals and the Al63Cu24Fe13 quasicrystal phase. The quasicrystal grains were of high crystalline quality equal to that of the best laboratory specimens, as demonstrated by the narrow diffraction peaks. The mechanism of their formation is yet uncertain. The specific composition of the accompanying minerals and the location where the sample was collected—far from any industrial activities—confirm that the discovered quasicrystal is of natural origin.
References
{{Commonscat
External links
Khatyrkite image and a TEM image of the quasicrystal
Native element minerals
Copper minerals
Aluminium minerals
Geology of Russia
Tetragonal minerals
Minerals in space group 140