Tourmaline

Tourmaline is 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. (DS9: "Our Man Bashir")