Maybe instead of making up yet another mystery element of the week, howzabout having them mining dilithium directly from the seawater? Weird planet, lots and lots of dilithium on the ocean floor, and thus unreachable by conventional means, but the dilithium leeches into the water, and can be collected and easily processed, in surprisingly large quantities, making it a very valuable resource for the Federation.
The dilemma comes in with the native animal life feeding on this sea dilithium ("sealithium?"
), and the sentient amphibian population feed on the animal life, which suddenly isn't doing so well now that this bunch of dilithium miners is sucking all the dilithium out of the water.
Natives attack, production drops, Starfleet panics and sends in Garrovick and the Exeter. Peaceful solution: Miners agree to extract the dilithium at a more sustainable level, so as not to threaten the native animal life, everyone goes back to their corners, and everyone's happy again.
I'd also suggest making "Atlantis" the name of the mining company, since these guys seem to specialize in oceanic operations. Name the planet something less cheesy, like Sigma Draconis III, or something like that.