Calcite from Durango, Mexico
Contributed by: Michael Crawford
Date: Jun 30th, 2025
Locality: Durango, Mexico (See on Mindat)
Size: 11.5 x 13 cm
Description:
The images show a calcite specimen from Durango, Mexico. False color images of ultraviolet fluorescence reveal three types of calcite in the specimen that are not seen in the daylight image or in the image taken under shortwave UV illumination. The specimen shows the typical visible red-orange fluorescence of calcite in shortwave illumination that is activated by manganese. The spectra shows the manganese activated fluorescence peaks at 619 nm. The three calcite types indicate three generations of formation. Numbers on the false color image correspond to numbers on the spectral plots.
The false color UV image shows that the base of the calcite specimen (area #1) has a bright bluish-white area of ultraviolet fluorescence. The spectrum of this calcite has a peak at 309 nm indicating a lead activator. Most of the calcite specimen has a dark green color in the false color image. The spectrum of this calcite has an ultraviolet fluorescent peak at 334 nm. This peak is likely activated by a rare earth element different from cerium seen in many calcite specimens from other locations. A cerium activated spectrum of calcite has two peaks in the ultraviolet at 340 nm and 364 nm. Most areas (#2) of the second type of calcite have dimmer ultraviolet fluorescence compared to the visible red fluorescence. There is a third area (#3) of brighter ultraviolet fluorescence with the same unknown activator. It has a lighter green color in the false color image. The brightness differences are likely caused by different activator concentrations.
Summary of luminescence responses:
Calcite (Mindat) (RRUFF)
- Fluorescence under Shortwave (255nm LED) UV light: Red