Trapezium Xenorhast and Cabochon Embolos (crafted versions of the two rare gems) are untradable. This appears to be a bug, in that for PoE and Fortuna the rare crafted gems were all tradable (Marquise, radian etc gems). Even Stellated Necrathene, which is one tier below the two, is tradable.
(to be clear, everyone I tried it with found them to be untradable. Although oddly Warframe.market lists them as being up for trade, so I'm unsure if they were tradable and now are not, or it was just assumed they'd be tradable).