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I recall Gandalf instructing Frodo in the lore of the Ring, and he mentioned that the Nine, the Seven and the Three, each had its proper stone or gem, but not so The One. It was unadorned and round, like one of the lesser rings.
Is there any mention of the gems on the Nine and the Seven? I know about the Three Elven Rings.
In my opinion, this is not a duplicate, as the other question queries about the make and material used for the rings. The gemstones have been mentioned very particularly by Gandalf, as possibly one of the proofs towards establishing the authenticity of Frodo's ring and its significance, and have been highlighted in the Elven rings. There has not been any mention of them in the literature commonly available.