Mineral containing one or more rare-earth elements as major constituents
Rare-earth ore, shown with a United States penny for size comparison
A rare-earth mineral contains one or more rare-earth elements as major metal constituents. Rare-earth minerals are usually found in association with alkaline to peralkalineigneous magmas in pegmatites or with carbonatiteintrusives. Perovskite mineral phases are common hosts to rare-earth elements within the alkaline complexes. Minerals are solids composed of various inorganic elements,[1] mixed through processes such as evaporation, pressure or other physical changes.[2][3] Rare earth minerals are rare because rare earth elements have unique geochemical properties that prevent them from easily forming minerals,[4] and are therefore not normally found in deposits large or concentrated enough for mining.[4] This is the reason they are called "rare" earths.[4][5] These elements have a wide range of uses from every day items to military technologies.[6] The minerals that do exist are often associated with alkaline magmas or with carbonatiteintrusives. Perovskite mineral phases are common hosts to rare-earth elements within the alkaline complexes. Mantle-derived carbonate melts are also carriers of rare earths. Hydrothermal deposits associated with alkaline magmatism contain a variety of rare-earth minerals.
These minerals contain the 17 rare earth elements, 15 of which are known as the lanthanides, the other two being scandium and yttrium.[7] The presence of these minerals can be a valuable indicator in geological surveys and mineral resource assessments.[8] There are over 160 rare earth minerals known, but only four of these occur in amounts suitable for mining.[9] They can occur in either primary or secondary deposits.[10]
Primary and secondary deposits
Primary deposits result from hydrothermal and igneous processes while secondary deposits are sedimentary and formed through weathering processes.[10] In the case of primary deposits, the minerals are generally found in the specific location where the elements came together to form the deposit.[11] Secondary deposits have undergone metamorphic or sedimentary processes in a location different from where the minerals were actually formed.[12][13] Depending on the type of deposit, various methods can be employed to extract the minerals from both primary and secondary deposits.[13][10]
Mined rare-earth minerals
Bastnäsite
Bastnäsite is a rare, semi-soluble carbonate mineral, primarily mined for its yttrium, used to make [14] magnets for speakers, microphones, communication devices, and many other modern necessities.[15][16] Bastnäsite deposits are found in China, Madagascar and the USA.[16]
It is a dense mineral that contains three carbonate-fluoride atoms. and typically forms luminous flattened crystals which have a warm yellow honey colour.
Laterite clays
Laterite is a class of materials which contain significant amounts of aluminium and iron.[18] They can form clays able to hold many minerals within them.[18] The weathering of rocks by leaching and oxidising conditions results in the formation of clay-like [18] minerals such as goethite, lepidocrocite, and hematite.[18] Some of them can hold rare earth minerals as well as iron, nickel and the alumina for which it is often mined.[19][20] Laterite results from the weathering of basalt.[19][20] It can make a stable basis for construction since it solidifies into rock when exposed to air.[20] However, its low fertility makes it unsuitable for agricultural use.[20]
Monazite
Monazite is a waxy mineral that is formed through the crystallization of igneous rocks and the metamorphism of clastic sedimentary rocks.[21] This mineral is typically mined in placer deposits, with gold commonly found as a byproduct.[21] Monazite contains many rare metals such as neodymium, cerium, lanthanum, praseodymium, and samarium, making it a critical material for renewable energy devices.[22][21] Monazite sand and deposits for mining are found in India, Brazil, and Australia.[23]
Loparite
Loparite is a mineral that is mined for the three rare (but not rare earth) elements: titanium, niobium, and tantalum it contains.[24] Major Loparite deposits can be found in Russia and Paraguay, and although it is present in other countries such as Canada, Norway, Greenland, and Brazil,[25] Russia remains the primary source for mining this mineral.[25] The elements in loparite make it useful for conductivity, aircraft assembly, and as a radioactive tracer.[24]
Jones, Adrian P., Francis Wall and C. Terry Williams, eds. (1996) Rare Earth Minerals: Chemistry, Origin and Ore Deposits, The Mineralogy Society Series #7, 372 pp. ISBN978-0-412-61030-1
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