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7 days agohttps://www.merriam-webster.com/dictionary/mineral kingdom
They are not a biological kingdom since they are inorganic. They stand outside of biology taxonomy in that sense. But they are still classified into a kingdom, or at least they were many many years ago when I was a little kid. Things change and I can easily be wrong and now minerals are also split up or something or put into “domain” or some other taxonomic level. Taxonomy is not my strong suit.
I edited my previous comment :)
The way I learned it was that you had to have some taxonomic class for inorganic things that grow (like crystals) as well. But its a long time ago, so I could be completely wrong, do not take me as an authority or anything.