Chukanovite is an iron(II)

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

mineral with the ideal chemical formula Fe⁺²₂(CO₃)(OH)₂. It is a member of the

rosasite Rosasite is a carbonate mineral with minor potential for use as a zinc and copper ore. Chemically, it is a copper zinc carbonate hydroxide with a copper to zinc ratio of 3:2, occurring in the secondary oxidation zone of copper-zinc deposits. It wa ...

mineral group and crystalizes in the monoclinic crystal system. Upon initial crystallization, it is typically pale green to colorless, but it takes on a brownish green hue after being altered at the surface. As a

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

product of

meteoritic iron Meteoric iron, sometimes meteoritic iron, is a native metal and Primitive rock, early-universe protoplanetary-disk remnant found in meteorites and made from the elements iron and nickel, mainly in the form of the mineral phases kamacite and taenit ...

, chukanovite is a relatively uncommon mineral on Earth, having only been discovered in the year 2000. However, it is commonly formed artificially as a

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

byproduct through the manufacturing of sand-deposited

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

Occurrence

Chukanovite was first discovered in weathered cavities of a meteorite which fell near the small village of Dronino, 350 km southeast of Moscow, Russia, but the mineral has since been found elsewhere in cavities of other iron-rich meteorites. It occurs primarily in association with

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

akaganeite Akaganeite, also written as the deprecated Akaganéite,Ernst A.J. Burke (2008):Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks. ''Mineralogical Record'', volume 39, issue 2. is a chloride-containing iro ...

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

, hibbingite, reevesite, honessite, and

kamacite Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. According to the International Mineralogical Association (IMA) it is considered a proper nickel-rich variety of the mineral native iron. The proportion iron:ni ...

, though the meteorites that contain chukanovite also tend to contain

taenite Taenite is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with a chemical formula of and nickel proportions of 20% up to 65%. The name is derived from the Greek ταινία for "band, ribbon" ...

and

chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can s ...

. Individual crystals form from a reaction between kamacite and cold water that is rich in dissolved

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

, during which they adopt a fibrous to acicular habit and grow to an average size of roughly 0.5 mm in length and 2-3 μm in thickness. Individual crystals tend to coalesce within the meteorite cavities into porous collections or crusts of

spherulites In petrology, spherulites () are small, rounded bodies that commonly occur in vitreous igneous rocks. They are often visible in specimens of obsidian, pitchstone, and rhyolite as globules about the size of millet seed or rice grain, with a dul ...

, each with a diameter of about 1 mm.

Physical properties

Crystals of chukanovite are pale green to colorless with a vitreous luster. If exposed to air for extended periods of time, chukanovite will weather over the course of a few months, becoming brownish green and then increasingly losing its color and luster as time passes. Throughout the weathering process, the mineral's streak will also change color, from white when unaltered to brownish yellow when weathered. Regardless of the degree to which it is weathered, chukanovite's cleavage remains perfect on , and its tenacity is always brittle. On the

Mohs scale of mineral 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 th ...

, chukanovite lies between 3.5 and 4.0, making it softer than

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

but harder than

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. Its density is 3.60 g/cm³.

Optical and Chemical properties

Chukanovite is optically biaxial negative with α = 1.673, β = 1.770, γ = 1.780, 2V(meas.) = 10°, and 2V(calc.) = 34°. The crystals are transparent and nonpleochroic, and exhibit a birefringence of δ=0.1070. The ideal chemical formula for chukanovite is Fe⁺²₂(CO₃)(OH)₂ but actual composition can vary and usually includes

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

and

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

. The

empirical formula In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, would simply be SO, as is th ...

, calculated on the basis of two metal cations, is (Fe⁺²_1.97Ni_0.02Mg_0.01)_Σ2.00(CO₃)_0.93(OH)_2.14•0.18H₂O. As a carbonate mineral, chukanovite effervesces readily in cold, dilute HCl solution.

Chemical composition

The table below lists the average composition of oxides in chukanovite.

X-ray crystallography

Chukanovite crystallizes in the monoclinic crystal system, within the 2/m point group and P2₁/a space group. Its unit cell consists of three unequal axes lengths with angles α = γ = 90°; β = 97.78°. The unit cell dimensions were measured via

x-ray powder diffraction An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 ...

and are a = 12.396 Å, b = 9.407 Å, c = 3.2152 Å, and Z = 4. The following chart tabulates the x-ray diffractogram results for chukanovite using conventional x-ray diffraction methods with Fe''K''α radiation (λ = 1.93 Å).

References