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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 peralkaline igneous complexes in pegmatites. This would be associated with alkaline magmas or with carbonatite intrusives. Perovskite mineral phases are common hosts to rare-earth elements within the alkaline complexes. Minerals are the solid composer of inorganic substances.^[1] They are formed through the atomic movement of fluid which can be derived from evaporation, pressure or any physical change.^[2] They are mostly determined through their atomic weight.^[3] The minerals that are known as 'rare' earth minerals are considered rare due to their unique geochemical makeup and properties.^[4] These substances are not normally found in mining affiliated clusters.^[4] Thus an indication of these minerals being short in supply and allocated their title as 'rare' earth minerals.^[4] Many rare-earth minerals include rare-earth elements which thus hold the same significant purpose of rare-earth minerals.^[5] Earth's rare minerals have a wide range of purposes, including defense technologies and day-to-day uses.^[6] This would be associated with alkaline magmas or with carbonatite intrusives. Perovskite mineral phases are common hosts to rare-earth elements within the alkaline complexes. Mantle-derived carbonate melts are also carriers of the rare earths. Hydrothermal deposits associated with alkaline magmatism contain a variety of rare-earth minerals. Rare-earth minerals are usually found in association with alkaline to peralkaline igneous complexes in pegmatites.

The following includes the relatively common hydrothermal rare-earth minerals and minerals that often contain significant rare-earth substitution:

Categorized

This particular group of minerals contains elements that are considered rare in our planet's makeup.^[7] To be classified as a rare earth mineral, a thorough examination of the element contained within it is mandatory.^[7] If an element can be classified as a rare-earth element, it is more likely to be classified as a rare earth mineral. This information can be valuable in various settings, such as geological surveys and mineral resource assessments.^[8] A rare earth element is categorized into sixteen metallic elements.^[8] There are over 160 rare earth minerals and only four of these minerals are mined.^[9] Most rare earth minerals occur in primary and secondary deposits.^[10]

Primary and secondary deposits

Primary deposits contain hydrothermal and igneous processes while secondary deposits are sedimentary and weathering processes.^[11] In the case of primary deposits, the minerals and metals are derived from a specific area, where the elements come together to form the deposit.^[12] This location is also where the mineral is produced.^[12] Derived elements move to a different location within secondary deposits where they undergo metamorphic or sedimentary processes, resulting in the formation of minerals.^[13] Mining extractions can benefit from the mineral processing of elemental deposits.^[14] Various methods, such as leaching and hydrothermal processes, can be employed to extract minerals.^[15] Both primary and secondary deposits yield elements and minerals for mining purposes.^[15] There are only four rare-earth minerals that are found in deposits that go through certain processes and require mining.^[16]

Mined rare-earth minerals

Bastnäsite

Bastnäsite is a carbonate mineral, that is primarily mined for its many purposes.^[17] Magnets made of bastnasite are used to create speakers, microphones, communication devices, and many other modern gadgets.^[18] This mineral is rare because it contains a large number of rare elements.^[19] This mineral can be classified as semi-soluble salt due to its limited solubility in water and capacity to form ionic bonds.^[19] Bastnäsite deposits are found in China and the USA.^[19]

Laterite clays

Laterite is considered to be a soil type which holds a significant amount of aluminium and iron.^[22] This soil type can form into clay, which holds many minerals within it.^[22] The weathering of rocks under leaching and oxidation conditions results in the formation of this mineral soil, which simulates clay.^[22] The minerals within this soil are goethite, lepidocrocite, and hematite.^[22] In recognition of the weathering process that these minerals require, they are classified as rare earth minerals.^[23] In addition to these rare minerals other elements are contained within this soil like substance such as iron and nickel.^[24] Thus having a red colour like soil through the oxidation of these minerals.^[24] Basalt is the source of laterite, which is a material that contains aluminum.^[23] Its high aluminum content is the reason it is mined.^[24] This clay-like dirt also makes a stable basis for construction since it solidifies into rock when exposed to air.^[24] However, the low fertility of this soil makes it unsuitable for agricultural use.^[24]

Monazite

Monazite is a waxy mineral that is formed through the crystallization of igneous rocks and the metamorphism of clastic sedimentary rocks.^[25] This mineral is typically mined in placer deposits, with gold commonly found as a byproduct.^[25] The rare earth element neodymium is found in monazite, making it a rare mineral.^[25] Moreover, monazite contains many other rare metals such as cerium, lanthanum, praseodymium, and samarium, making it a critical source of renewable energy.^[26] Recycled magnets can also be derived from these minerals due to the metals they contain.^[25] Monazite sand and deposits for mining are found in India, Brazil, and Australia.^[27]

Loparite

Loparite is a mineral that contains three rare elements: titanium, niobium, and tantalum.^[28] This is why it is often mined, as it is considered a rare-earth mineral.^[28] The deposits for loparite can be found in Russia and Paraguay, although it is also present in other countries such as Canada, Norway, Greenland, and Brazil.^[29] However, Russia remains the primary source for mining this mineral.^[29] The significance of loparite lies in its unique properties, which make it useful for conductivity, aircraft assembly, and as a radioactive tracer.^[28]

Rarity

Kyawthuite is a rare earth mineral due to its unique formation process.^[30] Unlike other minerals, it is created from a pegmatite deposit within an igneous rock.^[31] Its deep red-brown colour and high density come from the crystal assemblages within it.^[32] Its occurrence is very limited and the necessary pressure for formation is uncommon, making it quite scarce. The mineral contains lead, thallium, and oxygen that have undergone oxidation and is also composed of the rare metals bismuth and antimony.^[31] Interestingly, the mineral is named after Dr. Kyaw Thu, a former geologist at the University of Yangon who discovered it.^[31] It is found in the region of Myanmar Mogok.^[33]