Cubanite is a

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 ...

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 ...

sulfide mineral The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, th ...

that commonly occurs as a minor alteration mineral in

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

tic

sulfide deposit A sulfide deposit is an ore body or rock containing a great deal of sulfide minerals. Articles on this topic include: * Seafloor massive sulfide deposits * Sedimentary exhalative deposits *Volcanogenic massive sulfide ore deposit Volcanogenic ...

s. It has the chemical formula CuFe₂S₃ and when found, it has a bronze to brass-yellow appearance. On the

Mohs hardness scale 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 ...

, cubanite falls between 3.5 and 4 and has a

orthorhombic crystal system In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...

. Cubanite is chemically similar to

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mo ...

, however it is the less common copper iron sulfide mineral due to crystallization requirements. Cubanite occurs in high temperature

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

mineral deposits with

pyrrhotite Pyrrhotite is an iron sulfide mineral with the formula Fe(1-x)S (x = 0 to 0.2). It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it i ...

and

pentlandite Pentlandite is an iron–nickel sulfide with the chemical formula . Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of wei ...

as intergrowths with chalcopyrite. It results from

exsolution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

from chalcopyrite at temperatures below 200 to 210 °C. If cubanite is exposed to temperatures above 210 °C, it will transform into isocubanite. After this transformation, if it begins to cool, it will not revert to cubanite. Upon its transformation to isocubanite it will lose its highly magnetic property due to its change from an orthorhombic to a cubic crystal structure. Cubanite has been identified on chondrites and within dust grain samples and has improved the precision of copper isotope analysis.

Etymology and history

Cubanite comes from the Spanish word ''Cubano,'' or Cuban in English, and the suffix ''-ite'', when naming a mineral. Cubanite was first described in 1843 for its occurrence in the Mayarí-Baracoa Belt, HolguÍn Province,

Cuba Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...

. It may also be referenced as barracanite in some literature.

Association and alteration

As a minor alteration mineral, cubanite can only form when there is hydrothermal alteration of magmatic ores. The ores that are associated with cubanite are unaltered

ores that experience alteration to

millerite Millerite is a nickel sulfide mineral, Ni S. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general la ...

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

-chalcopyrite-cubanite ores, like those seen in the Bushveld Complex. For cubanite to form from chalcopyrite, a loss of copper relative to sulfur and iron and an increase in iron relative to sulfur must occur. This significant change in mineralogy results crystal structure change from tetragonal chalcopyrite to orthorhombic cubanite. With an increase in temperature above 210 °C, alteration continues and cubanite will transform into isocubanite, an isometric polymorph. There will be no transformation back to cubanite upon the cooling of the isocubanite.

Extraterrestrial cubanite

Although cubanite forms in hydrothermal mineral deposits, there are occurrences of cubanite that did not form on earth. Cubanite has been found in carbonaceous chondrite meteorites, specifically class CI-chondrites, as well as in cometary samples from NASA’s Stardust spacecraft. Data from the Itokawa asteroid, collected by the

Hayabusa was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis. ''Hayabusa'', formerly known as MUSES-C fo ...

spacecraft, indicated that a 2-micrometre grain of cubanite was found on the

S-type asteroid S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the secon ...

. This is the first time cubanite has been found on another asteroid that was not class C-type. However, further inspection of the sample revealed that the cubanite likely formed exogeneous to the Itokawa body.

Synthetic cubanite

Although synthetic and chondritic cubanite have structural variations, synthesis of cubanite still grants insight into the formation of CI-chondrites. Using a lab-based variant of hydrothermal recrystallization, temperatures between 150-200 °C, and a pH of 9, scientists were able to determine compositions needed to replicate CI-chondrite mineralogy. Experiments that began with copper + iron + sulfur,

covellite Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known t ...

troilite Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe(1-x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency whic ...

, and copper + sulfur + troilite all formed cubanite. Starting with troilite instead of iron metal reinforces previous studies that sulfides on Cl-chondrites are the resultant of oxidation of troilite by hydrothermal processes.

Copper isotope analysis

Due to its complex growth nature, Cubanite has been the test subject for instrumental preference in copper isotope microanalysis. It was found that ultra violet laser ablation multiple collector

inductively coupled plasma mass spectrometry Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is ...

(UV-fs-LA-MC-ICP-MS) improves precision in respect to copper isotopes, when compared to the use of near infrared (NIR-fs-LA-MC-ICP-MS) methods. ICP-MS

References

Sulfide minerals Copper minerals Iron minerals Orthorhombic minerals Minerals in space group 62 {{sulfide-mineral-stub