Petrified Wood – Chemnitz, Germany

Contributed by: Michael Crawford
Date: Oct 18th, 2026
Locality: Hilbersdorf quarries, Hilbersdorf, Chemnitz, Saxony, Germany (See on Mindat)
Size: 8.5 cm

Description:
This petrified conifer wood slab (Dadoxylon sp.) comes from Chemnitz, Saxony, Germany, and dates to the Permian Period. About 291 million years ago, volcanic ash and lapilli from the nearby Zeisigwald volcano buried the Chemnitz forest. Today, the Petrified Forest lies beneath a densely populated urban area, with its wood-bearing volcaniclastic layers about 20 feet below street level. As a result, new specimens are typically discovered only during construction.

Groundwater dissolved silica from the surrounding volcanic deposits and carried it into the wood, where chalcedony replaced the organic cells while preserving the wood’s anatomical structure. The groundwater also leached uranium from the volcanic ash, incorporating it into the chalcedony as uranyl ions. Trace uranyl ions cause green fluorescence under midwave and shortwave UV light. The fluorescence is brightest under shortwave UV, although a strong source is required to make it visible.

Chemnitz petrified wood is unusual because it is often mineralized with purple fluorite as well as chalcedony. The fluorite’s purple color results from colloidal calcium in its crystal structure and formed through deposition by radioactive fluids. Some fluorite in this slab fluoresces a relatively bright yellowish white under all UV wavelengths, possibly activated by organic material from the original wood.

The slab is approximately 8.5 cm in diameter.