Rare-earth mineral

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 magmas in pegmatites or with carbonatite intrusives. 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 carbonatite intrusives. 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.

Rare-earth ore, shown with a United States penny for size comparison

The following list includes the more common hydrothermal minerals that often contain significant rare earth elements:

• aeschynite-(Ce)
• aeschynite-(Y)
• allanite
• apatite
• bastnäsite
• britholite
• brockite
• cerite
• dollaseite-(Ce)
• fluocerite
• fluorite
• gadolinite
• monazite
• parisite-(Ce)
• parisite-(La)
• stillwellite
• synchysite
• titanite
• wakefieldite
• xenotime
• zircon

Categories

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.^[17] and typically forms luminous flattened crystals which have a warm yellow honey colour.^[17]

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]

Rarity

Kyawthuite is a rare mineral because the extreme pressure needed for its formation is very uncommon.^[26] Unlike other minerals, it is created from a pegmatite deposit within an igneous rock.^[27] Its deep red-brown colour and high density come from the crystal assemblages within it.^[28] The mineral contains lead and thallium that have undergone oxidation, as well as the rare metals bismuth and antimony.^[27] The mineral is named after Kyaw Thu, a former geologist at the University of Yangon who discovered it.^[27] It is found in the region of Myanmar Mogok.^[29]