Onyx

Taken all the way down to base materials, one Onyx is 2 crafting steps deep and needs 1 intermediate — Tuff Whetstone ×1 — which resolves to 2 distinct raw materials totalling 6 units, plus 14 crystals.

That bill outweighs 4,542 of the 13,602 recipes tracked here and 643 of the 2,216 Goldsmith ones, and 4,464 recipes nest deeper.

Only 7 of those crystals go into the final step; the other 7 are burned by the intermediates, so the real crystal cost is 14 Wind Crystal.

Every step is Goldsmith work, from a Lv 76 intermediate up to the Lv 80 finish, so one class covers the whole chain.

Both raw materials are gathered, and one of them is time-gated: Raw Onyx (0:00, 12:00). The widest gap between consecutive opening times is 12 Eorzean hours, about 35 real-world minutes.

Onyx is itself consumed by 61 further recipes, spanning four of the eight crafting classes.