Zenith Chronometer Rarest Luxury Men's Pocket Watch in Agate Case circa 1900

What you are showing here is indeed an original Zenith pocket watch with an agate case – a very rare collector's item. It is a model similar to the Chronomètre Zenith with a monocoque case (made from a single piece) of three-colored, banded agate, made around 1900–1910.

Such a watch was indeed the subject of an auction by Karl-Heinz Cortrie GmbH in Hamburg:
The lot described this exact piece as

“Pocket watch Chronometre Zenith, rare agate case, approx. Ø 52 mm, monocoque case made of stone, magnificent three-colored agate, bezel and pendant made of rose gold, lever movement in chronometer quality, enamel dial with Breguet hands, functional”

In the DGC-Uhrenforum this type of Zenith is also discussed, with indications that some examples were originally made for the Russian Tsar's court and only later went on general sale – making them among the most exclusive Zenith pocket watches ever  

Features of your example:

• Case: Black, banded agate with white layers (probably onyx variant)
• Dial: Enamel with blue Arabic numerals and small seconds
• Movement: High-quality Zenith hand-wound movement with lever escapement
• Special feature: Unique character, as each agate case has individual patterns.

These pieces are extremely rare (significantly rarer than gold or silver Zenith pocket watches) and are highly sought after today, especially by collectors of precision mechanical and lapidary luxury objects. Prices vary greatly depending on condition, but are often in the mid to upper four-figure range 

These Zenith pocket watches with agate cases were indeed series products in very small editions, not individual custom-made items. They are therefore regular Zenith models from around 1900–1910, but with an unusual case material that was rarely chosen.

According to auction descriptions and contemporary sources, they were sold under the name “Chronomètre Zenith”, mostly with a monocoque case made of banded agate in various shades (black-white, brown, grey, red). Inside were high-quality lever movements in chronometer quality, and the movements corresponded to the brand's top calibers of the time. A documented example can be found, for example, in the auction archive of Karl-Heinz Cortrie GmbH, where a watch with 3-color agate, rose gold bezel and original box was offered  

The DGC-Uhrenforum confirms that these agate models were produced in small numbers and sold through regular Zenith dealers – not exclusively for the Russian market, even if some were originally intended for the Tsar's court 

Thus, it can be said:

• Yes, series production, but extremely small and elaborate.
• Each watch is unique due to the individual agate structure.
• Today highly sought-after collector's items