Goethite PS Marcasite
Posted by: macadmin on 05.14.2020 | Filed under:

Goethite PS Marcasite

Specimen # 100907
Mineral: Goethite PS Marcasite
Location: Goethite Pseudomorph After Marcasite, White Desert, North of Farafra Oasis, Egypt
Size: 4.4 x 4.0 x 3.6 cm


Detailed Description

On this goethite pseudomorph after marcasite, the radiating spires of marcasite crystal forms on this one are really different – they are very sharp, with crystal groups branching off of the spires themselves. The crystal forms are particularly sharp for this habit at this locality – super definition. In excellent condition – a couple of missing spires are low and around the sides as I’d display this, so not easily visible (if at all) as displayed – otherwise no damage. Super specimen.

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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 uncommon. These specimens 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). Recent 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 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.

Additional information

Dimensions 44 × 40 × 36 cm