Yellow chrysoberyl is the third hardest material in the anniversary Royal Oak gem set, behind only ruby and blue sapphire, and on a 37 mm case that ranking matters more than it does at 41 mm. A smaller watch sits differently on the wrist, with the bracelet wrapping tighter and the outer links taking more contact against desks, cuffs and door frames, and every one of those links is set with stones. Chrysoberyl resists that better than the beryls, garnets, quartz, topaz and tourmaline that make up most of the set, and it holds a polish on its tables where softer species dull. The species is known almost entirely through its two exotic varieties, alexandrite with its colour change and cat's eye chrysoberyl with its single band of reflected light, and the plain transparent yellow material used here is the same mineral without either effect. It is the least recognised name among the ten and, on durability alone, arguably the best-chosen.
The case is 37 mm across and 10 mm thick in white gold, with the octagonal bezel gem-set in baguette-cut yellow chrysoberyls. The plain 37 mm selfwinding Royal Oak of the same generation measures 9.1 mm, so the complete setting adds nine tenths of a millimetre, less than the one and one tenth it adds at 41 mm, because the smaller stones require shallower channels. The eight hexagonal screw positions remain in place, interrupting the run of stones at fixed points that the setting is built around rather than through. The dial is white gold set with baguette-cut yellow chrysoberyls across its full surface, with no applied hour-markers. The stones are the dial. Only the white gold Royal Oak hands sit above them. The bracelet carries the same setting along its length, tapering from the case and closing on an AP folding clasp. The pairing produces an effect none of the other stones reproduce: the dial reads as gold-coloured while the case reads as a cool white metal, so a watch made from one metal and one mineral appears to be made from two metals. At 37 mm, with smaller stones and a denser field, that reading is stronger than at 41 mm because the individual baguettes are harder to resolve as separate objects.
The function set is hours, minutes and centre seconds. There is no date. An aperture would require cutting through a continuous stone surface and breaking the setting at the point where the run most needs to remain whole, and on a smaller dial the break would take a greater share of the field. Centre seconds keeps the three hands on a single axis and avoids the second circular interruption a subdial would impose. Time is read from hand position against the case, since the dial carries no markers. Yellow chrysoberyl is among the paler stones in the set, so white gold hands over a light warm field is a moderate pairing, better than pink tourmaline or blue topaz and weaker than ruby or emerald. The hands are located by shape and length as much as by contrast, which is inherent to giving the dial over entirely to stone.
The Royal Oak is the collection Audemars Piguet is built on, and the 37 mm anniversary references form a ladder in how far the setting is taken. The 15550 is plain at 9.1 mm, the 15551 carries a diamond-set bezel over an unset dial at the same height, and this reference sets dial, bezel and bracelet and reaches 10 mm. Ten stones were used: yellow chrysoberyl, ruby, blue sapphire, emerald, tsavorite, tanzanite, blue topaz, amethyst, pink tourmaline and orange spessartite. Each was issued at 37 mm here and at 41 mm at reference 15514, giving twenty references built on one construction across two sizes. Yellow and orange are the only two warm stones in the set that are neither red nor pink, which makes the chrysoberyl and spessartite references the closest comparison either one has. Both were also issued at 41 mm at reference 15514, and neither colour appears anywhere else in the ten, so the warm end of the set comes down to four references in total across the two sizes.
This reference suits a collector who chooses on properties rather than on names. Almost nobody outside gemmology will identify the stone, and a yellow chrysoberyl Royal Oak will be read as a yellow stone by most people who see it, which is either the point or the problem. For a buyer weighing the ten on how they will survive being worn, this is the strongest candidate after the two corundums, and at 37 mm, where the bracelet takes more contact, that advantage is real rather than theoretical. It appeals to someone who has considered all ten and decided on merit, and to someone who wants warm colour without the immediate recognition that a yellow diamond or a citrine-coloured stone would invite. The anniversary designation ties production to the occasion rather than to an open catalogue run.
