FMF - Friends of Minerals Forum, discussion and message board

[Mathias]

Dear Friends of Minerals,

A few months ago, I purchased a specimen with the following Label:

Goethite, Herdorf, Germany.

The specimen is heavy (4 kilo), 18 x 12 cm.
I can't find a similar specimen on Mindat.
The specimen has a layered structure and layers are approximately 1 cm thick.

Has anybody ever encountered a similar specimen before?
How does this structure form?

Thanks,
Mathias

[Tobi]

Hi Mathias,

Herdorf is not one single locality but a mining area with several mines, the most famous is for sure Wolf Mine where the legendary rhodochrosites come from. I don't know for sure if this specimen is from that area but iron minerals like goethite or limonite are common there in different shapes so maybe the information is correct, not sure.

Regards
Tobi

[Matt_Zukowski]

It looks like petrified wood. Any possibility it is wood replaced in part by Fe/Mn oxides/hydroxides?

[Roger Warin]

The needle crystals are vertically associated and form layers of successive deposits.
In addition, the wood does not contain horizontal interruptions.