A gemstone was a mineral crystal. Considered valuable dure to rarity, these could be used to make types of jewelry.
In the 24th century, gemstones were considered valuable by Betazoids, the Bajorans of Sidau village, the Wadi and the Jibetians. (TNG episode: "Haven", DS9 episodes: "The Storyteller", "Move Along Home", DS9 novel: The Long Night)
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