Khatyrkite
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| Khatyrkite | |
|---|---|
 Khatyrkite sample. | |
| General | |
| Category | Native element class, alloy |
| Formula | (Cu,Zn,Fe)Al2 |
| IMA symbol | Ktk[1] |
| Strunz classification | 1.AA.15 |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Space group | I4/mcm |
| Unit cell | a = 6.06, c = 4.87 [Å]; Z = 4 |
| Identification | |
| Color | Gray-yellow (reflection) |
| Crystal habit | Prismatic crystals and intergrowths with cupalite |
| Cleavage | {100}, distinct |
| Tenacity | Malleable |
| Mohs scale hardness | 5–6 |
| Luster | Metallic |
| Streak | Dark gray |
| Diaphaneity | Opaque |
| Specific gravity | 4.42 (calculated) |
| Optical properties | Distinctly anisotropic, grayish yellow to brownish red |
| References | [2][3][4] |
Khatyrkite (/ˈkætiərkaɪt/ KAT-ee-ər-kyte)[5] is a rare mineral which is mostly composed of copper and aluminium, but may contain up to about 15% of zinc or iron.[4][6] Its chemical structure is described by an approximate formula (Cu,Zn)Al2 or (Cu,Fe)Al2. It was discovered in 1985 in a placer in association with another rare mineral cupalite ((Cu,Zn,Fe)Al). These two minerals have only been found at 62°39′11″N 174°30′02″E / 62.65306°N 174.50056°E in the area of the Iomrautvaam, a tributary of the Khatyrka river, in the Koryak Mountains, in Anadyrsky District (former Beringovsky District), Chukotka, Russia. Analysis of one of the samples containing khatyrkite showed that the small rock was from a meteorite.[7] A geological expedition has identified the exact place of the original discovery and found more specimens of the Khatyrka meteorite.[8][9] The mineral's name derives from the Khatyrka (Russian: Хатырка) zone where it was discovered.[10] Its type specimen (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.[2][3][6]
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.[11] It was found later that iron can be substituted for zinc.[6] The mineral is opaque and has a steel-gray yellow tint in reflected light, similar to native platinum. 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 units 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.[11]
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 was formed in a high-energy impact involving the object that became the Khatyrka meteorite.[3][6][12]
- Phillip Broadwith (4 June 2009). "Natural quasicrystals discovered". Chemistry World.
