Columbite
Template:Short description Template:Infobox mineral Columbite, also called niobite, niobite-tantalite and columbate, with a general chemical formula of Template:Chem2, is a black mineral group that is an ore of niobium. It has a submetallic luster, a high density, and is a niobate of iron and manganese. Niobite has many applications in aerospace, construction and the medical industry. Dating columbite minerals is primarily completed by uranium lead (U-Pb) dating, a slow process.
Columbite has the same composition and crystal symmetry (orthorhombic) as tantalite.<ref>Template:Cite journal</ref> In fact, the two are often grouped together as a semi-singular mineral series called columbite-tantalite or coltan in many mineral guides. However, tantalite has a much greater specific gravity than columbite, more than 8.0 compared to columbite's 5.2.<ref>mindat.org Tantalite</ref> The formation of columbite depends on the concentrations of metals present that affect the crystalline structure of the mineral and the environmental impact.
Columbite is a polymorph of tapiolite; they have the same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite.<ref>P. Cerny et al. "The tantalite-tapiolite gap: natural assemblages versus experimental data" Canadian Mineralogist 30 (1992) 587 free download</ref> The largest documented single crystal of columbite consisted of plates Template:Convert thick measuring Template:Convert.<ref>Template:Cite journal</ref>
Columbite contains varying amounts of thorium and uranium, making it radioactive.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Coltan, a tantalum dominate species of columbite, is often mined by artisan and small scale miners with risks to the environment and human health due to unregulated working conditions.
History and etymologyEdit
This mineral group was first found in Haddam, Connecticut, in the United States.<ref>Template:Cite journal</ref> The occurrence of columbite in the United States was made known on April 13, 1905, through the publication of research into the composition of an older specimen, presumably stemming from John Winthrop (1606–1676), first Governor of the Connecticut Colony and avid mineral collector. Amidst 600 other samples, the relevant specimen had been donated by the Governor's namesake and grandson, John Winthrop (1681–1747) to Hans Sloane, President of the Royal Society of London, upon Winthrop's becoming a Fellow of the Royal Society in 1737.<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
In 1801, Charles Hatchett had discovered the element niobium in the same specimen,<ref> Template:Cite journal</ref> which he had named columbium in honour of explorer Christopher Columbus.<ref> Template:Cite book</ref>
Columbite speciesEdit
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Columbite forms opaque crystals that are black to dark brown in colour.<ref name=":1">Template:Cite journal</ref> The formation of the crystals vary based on the species present.
Columbite forms a series with the tantalum-dominant analogue ferrotantalite and the manganese-dominant analogue manganocolumbite. Manganocolumbite has a chemical formula of (Mn, Fe)(Nb, Ta)2O6, often with small concentrations of tantalum and iron. Manganocolumbite is often found in pegmatites, course-grained igneous rocks.<ref name=":1" />
The iron-rich member of the columbite group is ferrocolumbite, FeNb2O6, and small concentrations of tin and tungsten may be present. This species of columbite is often found in pegmatites as course-grained igneous rocks.<ref name=":1" />
Yttrocolumbite is the yttrium-rich columbite with the formula Template:Chem, is a radioactive mineral found in Mozambique.<ref>Template:Cite journal</ref> This mineral forms due to pegmatites and rare-metal granites.<ref name=":1" />
StructureEdit
Columbite atoms form an octahedral structure where niobium or tantalum atoms surround an oxygen atom. Overall, Columbite forms orthorhombic crystals which give approximate lengths of the crystal axes as a ≈ 14.27, b ≈ 5.73, and c ≈ 5.06 Å.<ref name=":2">Template:Cite journal</ref> Different columbite species such as manganocolumbite or ferrocolumbite can change the lengths of the crystal axes.<ref name=":2" />
Since columbite can form species with other minerals, the physical properties of the mineral can change. When ferrocolumbite is introduced to heat, an equal expansion of the ‘a’ and ‘b’ axis occurs.<ref name=":2" /> In addition, due to the size of the ions and the overall structure, ferrocolumbite is more compressible than manganocolumbite.<ref name=":2" /> When manganocolumbite is introduced to heat, an expansion of the ‘a’ axis occurs resulting in an uneven change to the structure.<ref name=":2" />
ApplicationsEdit
When niobite is extracted from columbite, in the ore refining process, applications can be observed in the aerospace, construction, and medical industry.<ref name=":5">Template:Cite journal</ref> In the aerospace industry, super alloys can be created. Super alloys from niobite create a low mass, and high resistance material often used in spacecrafts.<ref name=":5" /> In construction, some high-strength low-alloy (HSLA) steel is created from niobite.<ref name=":5" /> In addition, niobite extracted from columbite can be used to create electronic components used in medical equipment such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR).<ref name=":5" />
FormationEdit
Columbite is often found in pegmatite and alluvial deposits, as well as granitic rocks.<ref name=":0">Template:Cite journal</ref> Columbite minerals are mainly composed of magnesium, iron, niobium, and tantalum where trace amounts of tin, titanium, and scandium have been observed.<ref name=":0" /> The overall composition of columbite influences the crystalline structure resulting in different formation processes. Currently, there are two prominent theories for the formation of columbite. One theory was developed due to a strong attraction of niobium and tantalum, within columbite, to silicate melts found in the earth's crust or mantle.<ref name=":6">Template:Cite journal</ref> In addition, the presence of magma forms columbite by undergoing two crystallization processes.<ref name=":1" /> The first crystallization process creates a niobium core and the second crystallization process creates a tantalum rim.<ref name=":1" /> This theory is prominent due to the texture of the mineral during the fluid stage, and the magmatic fractional crystallization that occurs during formation.<ref name=":6" /> Another prominent theory of the formation of niobium and tantalum, in Columbite minerals, occurs due to hydrothermal fluids.<ref name=":6" /> This theory suggests that hydrothermal fluids interact with columbite during formation and as a result irregular crystals are formed.<ref name=":1" />
It is possible that both theories work in conjunction with one another to form columbite minerals as well as different species of columbite such as mangancolumbite, ferrocolumbite, and yttrocolumbite.
Environmental impactEdit
Columbite minerals have the potential to be radioactive due to trace amounts of uranium and thorium. Radioactive minerals are unstable due to the emission of radiation which causes negative impacts to the environment and human health. Each country has different laws regarding the transportation of radioactive material.<ref name=":7">Template:Cite journal</ref>
When mining columbite, contamination of ground and surface water are a concern due to the presence of heavy metals in waste rock. In addition, waste rock can lead to acid mine drainage which can affect ground and surface water.<ref name=":7" /> To obtain pure columbite, a large quantity of waste rock is produced, leading to negative impacts to the surrounding environment.<ref name=":7" />
During the extraction of niobite or tantalum from columbite, strong acids at high temperatures are used that have negative impacts to the environment. Hydrofluoric acid and sulfuric acid are used in the ore refining processes between temperatures of 250-300oC.<ref name=":8">Template:Cite journal</ref> These acids can cause soil acidification, air pollution, and water pollution that, in turn, affects ecosystems. Current technology, in the ore refining of columbite, is not selective which leads to impurities present in refined Columbite samples.<ref name=":8" /> To remove impurities, a greater concentration of acid is required, leading to a greater potential of environmental hazards.<ref>Template:Cite journal</ref>
DatingEdit
There are three applications to dating columbite group minerals each with advantages and disadvantages. These methods are uranium lead (U-Pb) dating, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS). The U-Pb method, can determine the location, and age of a columbite mineral group by the U/Pb ratio.<ref name=":3">Template:Cite journal</ref><ref name=":4">Template:Cite journal</ref> This method is often paired with isotope dilution-thermal ionization mass spectrometry (ID-TIMS) to increase precision.<ref name=":3" /><ref name=":4" /> The LA-ICP-MS method is used in situ to date columbite-tantalite minerals with less than five percent error on the isotopic ratio of uranium and lead.<ref name=":4" /> The SIMS method has a high spatial resolution and has a high accuracy in measuring lead isotopes in columbite minerals.<ref name=":4" /> The LA-ICP-MS and SIMS method are not commonly used due to the lack of certified reference material.<ref name=":4" />
Artisanal and small scale miningEdit
Artisanal and small-scale mining provides jobs for millions of people but typically has negative impacts to human health and the environment.<ref name=":9">Template:Cite journal</ref> This type of mining is executed by small groups of people, typically under a larger mining cooperation, with simple extraction equipment.<ref name=":10">Template:Cite journal</ref> This simple extraction equipment can include pickaxes, shovels, basins, and minimal heavy machinery.<ref name=":10" /> Coltan, the tantalum dominant species of columbite, is often mined artisanally due to its vast applications in electronics.<ref>Template:Citation</ref> Artisanal and small-scale mining of materials are common in regions such as Africa, Asia, Oceania, Central American, and South America.<ref name=":10" /> While this type of mining is important for local economies and livelihood, it is often unregulated, which leads to illegal mining and unsafe working conditions. Due to unregulated conditions, the mistreatment of artisanal miners, violence, illegal trading, and sometimes child labour can occur.<ref name=":10" /> In addition, long term health effects are common when mining coltan, due to the presence of radioactive material within the mineral.<ref name=":9" /> In countries such as Sierra Leone, Liberia, and the Democratic Republic of the Congo, lucrative trading of minerals, such as coltan, has occurred due to lack of state control of artisanal and small-scale mining in the region.<ref name=":10" />
Further readingEdit
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External linksEdit
Template:Manganese minerals Template:Ores Template:Authority control