Description
Detailed Description
A super pseudomorph of goethite after marcasite, with well-defined crystals all around – lustrous and a deep brown, almost black. It features one main large crystal ball and a second small ball of crystals that are so rounded they’re almost not discernible. Of the many habits of these White Desert pseudomorphs, my friend Tracy Kimmel used to call the habit of the large ball the “mace head” habit. In excellent condition, slightly polished by the sands of the White Desert.
Please Note: the colour representation in the still photograph has been carefully calibrated and adjusted to show an accurate rendition of this specimen in daylight (shade). The colours in the video are not similarly adjusted.
About These White Desert Pseudomorphs
This locality has been known for a number of years and pseudomorph specimens have come out once in a while. The pseudomorphs occur within the Cretaceous Khoman Chalk, from which the White Desert derives its name. Most crystals have typically been fairly indistinct, and to date sharp specimens have been relatively uncommon. These specimens, collected in 2013 and 2014, are remarkable for their relatively sharp marcasite crystal forms in aesthetic crystal clusters.
Over the years, these pseudomorphs have been variously labeled hematite, goethite and limonite (the latter no longer a valid mineral species name, but is a term still used in reference to unidentified iron hydroxides, so its use has not been incorrect). Work by Hannah Allen at Hamilton College has confirmed that the White Desert pseudomorphs are predominantly goethite. The small white grains lodged in among the crystal blades are barite, calcite and gypsum. (Allen, Hannah M., Pseudomorphed Mineral Aggregates of the Khoman Chalk, Western Desert, Egypt, Geological Society of America Abstracts with Programs. Vol. 46, No. 2, p.66 (2014)).
Although pseudomorphs after cubic and cuboctahedral pyrite crystals have also been found in the Khoman Chalk, the pseudomorphs after marcasite are usually more dramatic. These pseudomorphs are excellent specimens featuring beautiful marcasite crystal morphology, showing habits and forms exhibited by the crystallized marcasite specimens from the famous occurrences at Cap-Blanc-Nez, Pas-de-Calais, France.
