Plumbogummite and Pyromorphite – Laohuan Mine, Guangxi, China

Contributed by: Michael Crawford
Date: Jul 3rd, 2026
Locality: Laohuan Mine, Gongcheng Co., Guilin, Guangxi, China (See on Mindat)
Size: 7 x 9 cm

Description:
This is a specimen of plumbogummite (PbAl₃(PO₄)(PO₃OH)(OH)₆) and pyromorphite (Pb₅(PO₄)₃Cl). The location on the label that came with the specimen says Yangshuo Mine, Yangshuo County, Guangxi, China. The November-December 2022 issue of The Mineralogical Record has an article describing these specimens and the correct location for these specimens is 10km north of the Yangshuo Mine at the Laohuan Mine, Gongcheng County, Zhuang Autonomous Region, Guangxi, China. The article has many pictures of plumbogummite-pyromorphite specimens, but there are no images of fluorescence. The spectacular fluorescence of these specimens comes from exposure to midwave UV illumination.

The plumbogummite and pyromorphite form in the oxidized zone of a lead deposit. The pyromorphite formed first and then the blue gray plumbogummite coated and replaced the yellow pyromorphite. Several crystals have a core of pyromorphite with a coating of plumbogummite.

The specimen has the brightest fluorescence under midwave UV illumination. The plumbogummite fluoresces green due to uranyl (UO₂²⁺) activation. The uranyl activation is clearly shown in emission spectra with the sharp peaks in the green region at 500 nm, 519 nm, 542 nm and 568 nm. These peaks occur in all plumbogummite spectra taken under 4 wavelengths of illumination (405nm laser, 365nm LED, 305nm LED, and 255nm LED). The longwave spectrum of plumbogummite has a broad peak centered at 449 nm and ripples on the flank of broad peak caused uranyl activation. The activator for the broad peak may be lead, possibly titanium substituting for aluminum, or unknown. The longwave image shows the blue gray plumbogummite fluorescence related to this broad peak. The color of the plumbogummite fluorescence changes to pale green under MW and SW illumination.

A midwave emission spectrum shows a broad peak with a maximum at 568 nm. The flank of the broad peak has ripples that are likely caused by uranyl activation. The SW image of the pyromorphite fluorescence appears more orange compared to the MW image. The SW fluorescence is not bright enough for me to acquire a spectrum, so I cannot speculate on why the fluorescent color shifts to a longer wavelength. The yellow fluorescence of pyromorphite is activated by europium according to fluomin.org, but a rare earth would produce a sharper peak. Lead (Pb²⁺) or manganese (Mn²⁺) are also potential candidates for fluorescent activation.