Columbite, also called niobite, niobite-tantalite and columbate, with a general chemical formula of , 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 dating, a slow process.
Columbite has the same composition and crystal symmetry (orthorhombic) as tantalite. 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. 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. The largest documented single crystal of columbite consisted of plates thick measuring .
Columbite contains varying amounts of thorium and uranium, making it radioactive. 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 etymology
This mineral group was first found in Haddam, Connecticut, in the United States. 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.
In 1801, Charles Hatchett had discovered the element niobium in the same specimen, which he had named columbium in honour of explorer Christopher Columbus.
Columbite species
left|thumb|Yttrocolumbite; a species of columbite|146x146px
Columbite forms opaque crystals that are black to dark brown in colour. 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)<sub>2</sub>O<sub>6</sub>, often with small concentrations of tantalum and iron. Manganocolumbite is often found in pegmatites, course-grained igneous rocks. This mineral forms due to pegmatites and rare-metal granites. Different columbite species such as manganocolumbite or ferrocolumbite can change the lengths of the crystal axes. 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. Columbite minerals are mainly composed of magnesium, iron, niobium, and tantalum where trace amounts of tin, titanium, and scandium have been observed. In addition, the presence of magma forms columbite by undergoing two crystallization processes.
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. 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.
Dating
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. This method is often paired with isotope dilution-thermal ionization mass spectrometry (ID-TIMS) to increase precision. This type of mining is executed by small groups of people, typically under a larger mining cooperation, with simple extraction equipment. This simple extraction equipment can include pickaxes, shovels, basins, and minimal heavy machinery. Artisanal and small-scale mining of materials are common in regions such as Africa, Asia, Oceania, Central American, and South America.