Palygorskite from cave sediments: case study from Wadi Haqil, United Arab Emirates
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ORIGINAL PAPER
Palygorskite from cave sediments: case study from Wadi Haqil, United Arab Emirates Nadja Zupan Hajna 1 & Roman Skála 2 & Asma Al-Farraj 3 & Martin Šťastný 2 & Pavel Bosák 2
Received: 11 November 2015 / Accepted: 12 October 2016 # Saudi Society for Geosciences 2016
Abstract The x-ray powder diffraction identification of clay minerals both in bulk samples and in separated clay fraction confirmed the presence of palygorskite in samples of cave sediments from Wadi Haqil (the western slopes of Musandam Mountains; Ras Al-Khaimah Emirate, UAE). Samples contain quartz, gypsum, smectite, kaolinite, calcite, and palygorskite, some of them chlorite, illite, feldspars, and goethite. Calcite dominates in most samples; smectite prevails in clay fraction. After heating, the 001 reflection of chlorite shifts to higher diffraction angles and its intensity decreases; these features indicate that the chlorite represent a Fedominant species. Unit-cell dimensions of major phases as refined by the Rietveld method are in agreement with literature data. Chemical composition of palygorskite was derived from unit-cell dimensions as follows: MgO content is 11– 14 wt% and Al2O3 10–13 wt%. Clay mineralogy is only hard to ascertain from the scanning electron microscope (SEM) images even after being combined with the energydispersive spectrometer data. The SEM was also used to
* Nadja Zupan Hajna [email protected] Roman Skála [email protected] Asma Al-Farraj [email protected] 1
Karst Research Institute ZRC SAZU, Titov trg 2, Postojna, Slovenia
2
Institute of Geology of the CAS, v. v. i., Rozvojová 269, 165 00 Praha 6, Czech Republic
3
Emirates Geographical Society, P.O. Box 4368, Ras Al-Khaimah, United Arab Emirates
characterize gypsum grains; they often display flow deformation features. Studied cave sediments represent palygorskitebearing weathering products and desert soils re-deposited from the cave surroundings by slope processes and wind and/or surface runoff. The mixture with other clay minerals, quartz, feldspars, etc. supports this interpretation. Finegrained quartz fraction is probably wind-blown. Gypsum and calcite are the precipitates (crusts and/or cements), although gypsum can also be re-deposited from omnipresent gypsum-cemented surface sediments. Keywords Palygorskite . Gypsum . Cave sediments . X-ray powder diffraction . Scanning electron microscopy . Ras Al-Khaimah Emirate
Introduction The joint expedition of the Karst Research Institute ZRC SAZU (Slovenia) and the United Arab Emirates University have visited the Musandam Mountains (Ras Al-Khaimah Emirate, UAE) with the aim to prospect and explore karst and caves. Expedition investigated several dry valleys (wadis), caves and karst springs (Al-Farraj et al. 2014). During field work, several small caves were found. Many narrow and long channels were partly filled by sediments, like some other caves in a broader region (cf. Audra et al. 2016). One of the most interesting locations of sedimentfilled caves was found at the entrance to the Wadi Haqil (UAE). Sh
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