Occurrence state
Rare earth elements exist mainly in the form of minerals in the earth's crust

As the basic elements of minerals, rare earth occurs in the crystal lattice of minerals in the form of ionic compounds, which constitutes an essential component of minerals. These minerals are usually called rare earth minerals, such as monazite, bastnaesite, etc.

As impurity elements of minerals, they are dispersed in rock forming minerals and rare metal minerals in the form of isomorphism replacement. These minerals can be called minerals containing rare earth elements, such as apatite and fluorite.

It is adsorbed on the surface or between particles of some minerals in ionic state. These minerals are mainly clay minerals and mica minerals. Rare earth elements in this state are easy to extract.
About 250 kinds of rare earth minerals have been found, but there are only 50-60 kinds of rare earth minerals with industrial value. At present, there are only about 10 kinds of rare earth minerals with mining value. At present, four kinds of minerals are mainly used for industrial extraction of rare earth elements - bastnaesite, monazite, phosphorite yttrium and weathering crust leaching deposit. The first three kinds of minerals account for more than 95% of the production of rare earth in the West. The content of LREE is higher in monazite and fluorite. The contents of hree and yttrium are higher, but the ore source is less than monazite.
In addition to China, there are Russia, Kyrgyzstan, the United States, Australia, India, Zaire and other countries with rare earth resources in the world; the main rare earth minerals are bastnaesite, ion adsorption type ore, monazite, yttrium phosphate, black rare gold, apatite, cerium niobium perovskite and so on. China, the United States, Russia, Kyrgyzstan, India, Brazil, Malaysia and other countries are mainly engaged in mining and mineral processing. In 1998, the world output of rare earth concentrate was more than 130000 tons (NATURAL tonnage). It is worth noting that Australia, India, South Africa and other countries with rare earth resources will overcome technical barriers and produce single rare earth products with high added value in the next five years. By then, the competition in the world market will be more intense.

Monazite
Crystal structure and morphology: monoclinic, orthorhombic columnar. The crystal is plate-shaped, and the crystal surface is often striped, sometimes columnar, conical or granular. Monazite is also known as lanthanite. Chemical composition and properties: (CE, La, y, th) [PO4]. The composition varies greatly. The content of rare earth oxide in mineral composition can reach 50-68%. Isomorphic mixtures are y, th, CA, [SiO4] and cerium [SO4]. Monazite is dissolved in H3PO4, HClO4 and H2SO4.

Physical properties: yellowish brown, brown, red, occasionally green. Translucent to transparent. Streaks are white or reddish yellow. It has strong glass luster. The hardness is 5.0-5.5. It's brittle. The specific gravity is 4.9-5.5. The electromagnetism is weak. It glows green in X-rays. It does not emit light under cathode rays.
Formation state: in granite and granite pegmatite; in rare metal carbonatite; in greisen and quartzite; in nepheline syenite, aegirine and alkaline syenite pegmatite; in Alpine vein; in migmatite; and in weathering crust and placer.

Usage: mainly used for extracting rare earth elements.
Origin: monazite resources with economic exploitation value are mainly alluvial or coastal placer deposits. The most important coastal placer deposits are in the coasts of Australia, Brazil and India. In addition, Sri Lanka, Madagascar, South Africa, Malaysia, China, Thailand, South Korea and North Korea all contain monazite heavy placer deposits.
Monazite production shows a downward trend in recent years. The main reason is that thorium in ore is radioactive and harmful to the environment.

Bastnaesite
Chemical composition and properties: (CE, LA) [CO3] F. The mechanical admixtures are SiO2, Al2O3 and P2O5. Bastnaesite is easily soluble in dilute HCl, HNO3, H2SO4 and H3PO4.

Crystal structure and morphology: hexagonal system. It is a compound trigonal biconical crystal. The crystal is hexagonal columnar or plate-shaped. Fine grained aggregate.

Physical properties: green or light brown, reddish yellow. Glass luster, grease luster, stripes are white, yellow, transparent to translucent. Hardness 4-4.5, brittleness, specific gravity 4.72-5.12, sometimes radioactive and weakly magnetic. It is transparent in thin film, colorless or yellowish under transmitted light, and does not emit light under cathode ray.
Formation state: occurring in rare metal carbonatite; granite and granite pegmatite; quartz vein related to granite syenite; quartz ferromanganese carbonate vein; placer.
Uses: it is an important mineral raw material for extracting cerium group rare earth elements. Cerium group elements can be used to make alloys to improve the elasticity, toughness and strength of metals. It is an important part for making jet aircraft, missiles, engines and heat-resistant machinery. It can also be used as a protective shell against radiation. In addition, cerium group elements are also used to make various colored glasses.

At present, the largest known bastnaesite is located in Bayan Obo mine, Inner Mongolia, China. As a by-product of iron ore mining, it is mined together with monazite, and its average content of rare earth oxide is 5-6%. The highest grade industrial bastnaesite deposit is the montanpas mine in California, USA, which is the only bastnaesite mainly mining rare earth in the world.

Xenotime
Chemical composition and properties: y [PO4]. The content of Y2O3 was 61.4% and P2O5 was 38.6%. Ytterbium, erbium, dysprosium and gadolinium are the main elements. There are zirconium, uranium, thorium and other elements instead of yttrium, accompanied by silicon instead of phosphorus. Generally speaking, the content of uranium in phosphorite is higher than that of thorium. The chemical properties of the phosphorite are stable.

Crystal structure and morphology: tetragonal system, tetragonal bipyramid, granular and massive.
Physical properties: yellow, reddish brown, sometimes yellow green, also brown or light brown. Streaks are light brown. Glass luster, grease luster. The hardness is 4-5, the specific gravity is 4.4-5.1, and it has weak polychromism and radioactivity.

Formation state: it mainly occurs in granite and granite pegmatite. It also occurs in alkaline granite and related ore deposits. It also occurs in placers.
Purpose: it can be used as mineral raw material for extracting rare earth elements in case of large amount enrichment.

Ionic rare earth ore
Eluviation type rare earth ore, i.e. ion adsorption type rare earth ore, is a new type of rare earth mineral peculiar to China. The so-called "ion adsorption" means that rare earth elements do not exist in the form of compounds, but are adsorbed in clay minerals in an ionic state. These rare earths are easily transferred into solution for strong electrolyte exchange, and mixed rare earth oxides can be obtained by direct leaching instead of crushing and mineral processing. Therefore, the characteristics of this kind of ore are: high content of heavy rare earth elements, high economic content, low grade, large coverage, mostly in hilly areas, suitable for manual and semi mechanized mining, simple mining and leaching process.

The weathering crust leaching deposit is mainly distributed in Jiangxi, Guangdong, Hunan, Guangxi, Fujian and other places in China.