Khatyrkite
Encyclopedia
Khatyrkite is a rare mineral which is mostly composed of copper
and aluminium
, but might contain up to about 15% of zinc
or iron
; its chemical structure is described by an approximate formula (Cu,Zn)Al2 or (Cu,Fe)Al2. It was discovered in 1985 in placers
derived from serpentine, in association with another rare mineral cupalite
({Cu,Zn,Fe}Al). Both minerals are thus far restricted to the area of Listvenitovyi Stream, in the Khatyrka
ultramafic (silicon
-poor) zone of the Koryak–Kamchatka fold area, Koryak Mountains
, Beringovsky District
, Chukotka Autonomous Okrug
, Far Eastern
Federal District
, Russia
. The mineral's name derives from the Khatyrka zone where it was discovered. Its holotype
(defining sample) is preserved in the Mining Museum
in Saint Petersburg
, and parts of it can be found in other museums, such as Museo di Storia Naturale di Firenze
.
. 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
symmetry with point group
4/m 2/m 2/m, space group
I4/mcm and lattice constants a = 0.607(1) nm, c = 0.489(1) nm and four formula unit
s per unit cell. 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
, that is they deform rather than break apart upon a strike; they have the Mohs hardness
is between 5 and 6 and Vickers hardness
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
, diopsidic clinopyroxene 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 is formed either upon meteoritic impact or in the deep earth mantle.
– aperiodic, yet ordered structure. The quasicrystal has a composition of Al63Cu24Fe13 which is close to that of a well-characterized synthetic Al-Cu-Fe material. This was the first quasicrystal found in nature and remains the only known naturally occurring example of a quasicrystal.
Quasicrystals were first reported in 1984 and named so by Dov Levine and Paul Steinhardt
. 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. 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
but no quasicrystals were found. Widening of the search eventually included khatyrkite. A sample of the mineral was provided by 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.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, but might contain up to about 15% of zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
or iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
; its chemical structure is described by an approximate formula (Cu,Zn)Al2 or (Cu,Fe)Al2. It was discovered in 1985 in placers
Placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early...
derived from serpentine, in association with another rare mineral cupalite
Cupalite
Cupalite is a rare mineral which is mostly composed of copper and aluminium, but might contain up to several percents of zinc or iron; its chemical structure is therefore described by an approximate formula Al or Al. It was discovered in 1985 in placers derived from serpentine, in association with...
({Cu,Zn,Fe}Al). Both minerals are thus far restricted to the area of Listvenitovyi Stream, in the Khatyrka
Khatyrka
-External links:*...
ultramafic (silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
-poor) zone of the Koryak–Kamchatka fold area, Koryak Mountains
Koryak Mountains
The Koryak Mountains are a mountain range in Far-Eastern Siberia, Russia, located south of the Anadyr River, and northeast of the Kamchatka Peninsula. Rivers Main and Velikaya have their sources in the Koryak Range. They are the second largest mountain range in all of Siberia....
, Beringovsky District
Beringovsky District
Beringovsky District was an administrative district of Chukotka Autonomous Okrug, Russia, which existed in 1957–2011. Municipally, together with Anadyrsky Administrative District, it was incorporated into Anadyrsky Municipal District...
, Chukotka Autonomous Okrug
Chukotka Autonomous Okrug
Chukotka Autonomous Okrug , or Chukotka , is a federal subject of Russia located in the Russian Far East.Chukotka has a population of 53,824 according to the 2002 Census, and a surface area of . The principal town and the administrative center is Anadyr...
, Far Eastern
Far Eastern Federal District
The Far Eastern Federal District is the largest of the eight federal districts of Russia, while being also the least populated, with a population of 6,291,900 . The Far Eastern Federal District was established in 2000 by then-President Vladimir Putin and is currently being governed by presidential...
Federal District
Federal districts of Russia
The federal districts are a level of administration for the convenience of the federal government of the Russian Federation. They are not the constituent units of Russia . Each district includes several federal subjects and each federal district has a presidential envoy...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. The mineral's name derives from the Khatyrka zone where it was discovered. Its holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
(defining sample) is preserved in the Mining Museum
Saint Petersburg Mining Institute
The G. V. Plekhanov Saint Petersburg State Mining Institute and Technical University is Russia's oldest higher education institute devoted to engineering...
in Saint Petersburg
Saint Petersburg
Saint Petersburg is a city and a federal subject of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea...
, and parts of it can be found in other museums, such as Museo di Storia Naturale di Firenze
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...
.
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 (Cu,Zn)Al2. 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 platinumPlatinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
. 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
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. 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 square base and height .There are two tetragonal Bravais...
symmetry with point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...
4/m 2/m 2/m, space group
Space 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...
I4/mcm and lattice constants a = 0.607(1) nm, c = 0.489(1) nm and four formula unit
Formula unit
A formula unit in chemistry is the empirical formula of an 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...
s per unit cell. 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
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
, that is they deform rather than break apart upon a strike; they have the Mohs hardness
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
is between 5 and 6 and Vickers hardness
Vickers hardness test
The Vickers hardness test was developed in 1924 by Smith and 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 tests since the required calculations are independent of the size of the...
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
Spinel
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...
, corundum
Corundum
Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red...
, stishovite
Stishovite
Stishovite is an extremely hard, dense tetragonal form of silicon dioxide. It was long considered the hardest known oxide; however, boron suboxide has recently been discovered to be much harder...
, augite
Augite
Augite is a single chain inosilicate mineral, 2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.-Characteristics:Augite is a solid solution in the pyroxene group...
, forsteritic olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, diopsidic clinopyroxene 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 is formed either upon meteoritic impact or in the deep earth mantle.
Relation to quasicrystals
Khatyrkite is remarkable by that it contains micrometre-sized grains of the only known naturally occurring quasicrystalQuasicrystal
A quasiperiodic crystal, or, in short, quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry...
– aperiodic, yet ordered structure. The quasicrystal has a composition of Al63Cu24Fe13 which is close to that of a well-characterized synthetic Al-Cu-Fe material. This was the first quasicrystal found in nature and remains the only known naturally occurring example of a quasicrystal.
Quasicrystals were first reported in 1984 and named so by Dov Levine and Paul Steinhardt
Paul Steinhardt
Paul J. Steinhardt is the Albert Einstein Professor of Science at Princeton University and a professor of theoretical physics. He received his B.S. at the California Institute of Technology and his Ph.D. in Physics at Harvard University...
. 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. 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
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
but no quasicrystals were found. Widening of the search eventually included khatyrkite. A sample of the mineral was provided by 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.