Although lutetium is (marginally) the rarest of the rare earth metals, thulium not only comes a second close but is also considerably more expensive. The reason why isn’t entirely clear. The Chinese refineries are remarkably tight-lipped about when it comes to divulging anything having to do with operations or sales data not just to their western customers but even to their Chinese colleagues as they’re all afraid information can be used to the market advantage of their competitors. In any case, both lutetium and thulium are metals with very low demand atop of their being so rare. Or perhaps due to it. Thulium has the added burden of being a finicky metal that is hard to work with as it very much tends to fall apart during tooling. The white glove treatment, of course, adds to the cost of manufacture.

Measures 15x8x0.94mm