Tourmaline
Tourmaline was a naturally-occurring gemstone found on Earth.

In the holodeck adventure Julian Bashir, Secret Agent, Bashir, posing as geologist Patrick Merriweather, had his knowledge of gemstones tested by Hippocrates Noah, showing him a statue encrusted with various kinds of gems, including tourmaline. Bashir successfully surmised that the statue contained not only tourmaline, but rubies, sapphires, and topaz, as well. ()

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de:Turmalin
Gemstones