An exceptional split ammonite from Indonesia, filled with dozens of open crystal-lined chambers and displaying dramatic fluorescence and phosphorescence under ultraviolet light.

Each half measures approximately 4.5" × 4.0" and has been cut to expose the internal structure of the fossil. Rather than being completely filled with solid mineral deposits, many of the original chambers remain open and are lined with delicate crystalline growth, creating a remarkable series of natural crystal pockets that follow the ammonite's spiral.

Under normal light, the specimen displays soft cream, pale gray, ochre, and muted reddish-brown coloration, with the darker interiors of the crystal chambers providing striking contrast. Under UV light, however, the mineralization transforms: areas throughout the fossil fluoresce in vivid yellow and red tones, highlighting structures and mineral deposits that are much more subtle in daylight.

The specimen is also phosphorescent. After the ultraviolet light source is removed, portions of the mineralization continue to glow briefly in green and red. Fluorescence occurs only while a specimen is exposed to ultraviolet radiation, while phosphorescence is the lingering emission of visible light after that excitation source has been removed.

Ammonites were extinct marine cephalopods with chambered shells used in buoyancy control. After burial, mineral-rich groundwater entered the empty shell chambers, allowing crystals to develop within the spaces once occupied by the animal's buoyancy system. Here, those mineralized chambers preserve both the anatomy of an ancient marine animal and the geological processes that continued long after its death.

The reverse is a beautifully prepared spiral, showcasing the exterior form and earthy reddish surface of the fossil. Together, the two sides offer dramatically different views of the same specimen: an understated ancient shell from the outside and an intricate network of crystal-filled, UV-reactive chambers within.

Details Specimen: Ammonite Size: Approximately 4.5" × 4.0" each half Weight: Approximately 424 g + 395 g (819 g total) Locality: Indonesia Two halves of a single ammonite Numerous natural crystal-lined chambers Fluorescent under UV light – yellow and red response Phosphorescent after UV exposure – green and red afterglow (see video) Natural exterior preserved on reverse One-of-a-kind fossil specimen

UV photographs show the specimen under ultraviolet light. Fluorescence and phosphorescence may vary depending on the wavelength and intensity of the UV light source used.

You will receive the exact ammonite pair pictured.