I will just note that they are mainly just a row on the periodic table! 
Heavy and light rare earth elements: The rare earth elements are often subdivided into "Heavy Rare Earths" and "Light Rare Earths." Lanthanum, cerium, praseodymium, neodymium, promethium, and samarium are the "light rare earths." Yttrium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are the "heavy rare earths." Although yttrium is lighter than the light rare earth elements, it is included in the heavy rare earth group because of its chemical and physical associations with heavy rare earths in natural deposits.
REE Production Chart: This chart shows China's dominance in the production of rare earth elements between 1994 and 2022. The United States was a significant producer through the 1990s, but low-priced materials sold by China forced mines in the United States and other countries out of operation. As China limited exports, and prices increased rapidly in 2009 and 2010, mines in Australia and the United States became active again. In 2018, data from Burma / Myanmar became available, causing an increase in production that may have been present but unreported prior to 2018. Graph by Geology.com using data from the United States Geological Survey.
https://geology.com/articles/rare-earth-elements/
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