Rare Earth Elements (REE) are named so because when they were discovered, they were thought to be extremely non-abundant.
However, this is not the case. REEs are very abundant in the earth’s mantel, but they are often not found in large enough deposits for them to be mined profitably.
On top on this, the extraction and refining process to turn ore into pure mineral powders is very complicated and cost intensive.
For this reason, the rarity of REEs comes from their availability and difficulty to produce in large quantities, rather than their general existence on earth.
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