Easily look-uppable @ Wikipedia or Google.
There are 17 rare earth elements, they are actually not all that crazy rare but they are hard to separate from each other and they only occur in certain geo locations.
I know of a couple of research efforts to reprocess coal mining waste to recover rare earths. Currently very hard to do technically & economically.
Sometimes questions are asked to encourage seekers. It’s a teachers trick. Lots of people speak without knowing what the background is. You will notice later links are provided for those who don’t bother to look up the background.