Adamite and Fluorite from the Ojuela Mine, Durango, Mexico

Contributed by: Michael Crawford
Date: Feb 16th, 2026
Locality: Ojuela Mine, Mapimí, Mapimí Municipality, Durango, Mexico (See on Mindat)
Size: 6 x 6 cm

Description:
A specimen of fluorite crystals (CaF₂) and adamite (Zn₂(AsO₄)(OH)) on a limonite matrix from the Ojuela Mine, Mapimi, Durango, Mexico. The fluorite fluorescence is brightest under longwave UV illumination. Its fluorescence is quite dim under midwave and shortwave UV light. The longwave fluorescence is zoned with cubic cores that are blue and rims that are red. The blue fluorescence is activated by europium (Eu2+) replacing calcium. The longwave emission spectrum has a peak at 420 nm.

The emission spectrum of the red fluorescence has a broad peak with a maximum in the infrared at 733 nm. The false color image highlights the rims of the fluorite cubes with the infrared fluorescence. This red and infrared fluorescence is likely caused by crystal defects called M-centers. A M-center consists of two adjacent vacancies of fluorine atoms. The vacancies are stabilized and charge balanced by a nearby sodium ion that either replaces a calcium atom or is interstitial. The M-centers are formed by naturally occurring radiation that caused the formation of crystal lattice defects. The fluids that deposited the fluorite were radioactive, but there is no residual radioactivity in the fluorite. The radioactivity also causes the purple color of the fluorite. The purple color is caused by colloidal calcium, not the M-center.

The green fluorescence of adamite is activated by uranyl ions. It glows brightly under all wavelengths of UV light. Adamite’s emission spectrum has sharp peaks at 507 nm, 528 nm, and 550 nm.