Mineralogical and chemical characterization of sepiolite occurrences at Karapinar (Konya Basin, Turkey)

Abstract

The Konya region in central Anatolia is covered by Pliocene-Late Pleistocene sediments and volcanites related to the sediments NNW of Karapınar, Turkey. In the area, the Upper Miocene-Quaternary Üzecek Dağı and Karacadağ volcanites are generally of the same age and formed from magmas of similar composition. The Karapınar formation is brown to whitish-beige, partly fossiliferous and consists of limestone, marl, claystone and, locally, sandy layers. Silica-rich lenses, nodules and layers are observed in the upper strata which locally contain sepiolite-rich layers. The mineralogical composition of sepiolite samples taken from the area was determined by powder X-ray diffractometry, while the abundance of major-element oxides was measured by X-ray fluorescence spectrometry. The crystallographic and morphological properties of samples were determined by means of scanning electron microscopy and energy dispersive spectroscopy. Samples were taken from three sections and from random locations. Mineral assemblages in the same stratigraphic position are generally similar in the three sections, while the thickness of the individual beds varies between the sections. Dolomite and calcite are the main carbonate minerals in the sections. Sepiolite occurs primarily with dolomite and, locally, dolomite and calcite, and less commonly with just calcite. Generally, quartz, feldspar and mica are found, especially in the upper parts of the sections where tuff is abundant. CaO and MgO dominate the major-element oxides. The CaO content is between 1 and 30% while MgO is 3–21%. Al2O3 and SiO2 are generally higher in the sepiolitic and tuffitic layers. Al2O3 is <3% and SiO2 is between 15–18% in the sepiolitic layers. The average structural formula of sepiolite was calculated as: (Mg7.00Al0.44Fe0.18)(Si11.71Al0.29)O30 (OH)4(OH2)4Ca0.13K0.09Na0.01. Sepiolite occurs as fibers and dolomite as subhedral or euhedral crystals. It is considered that sepiolite was formed either by conversion of dolomite or by direct precipitation from solution under alkaline and saline conditions in the Karapınar paleolake. The paleolake was saturated with respect to Mg, Ca and Si derived from groundwater that percolated along fracture systems.

Ni-sepiolite-falcondoite in garnierite mineralization from the Falcondo Ni-laterite deposit, Dominican Republic

“…XRD patterns of the oriented-mounts of samples showed a slight expansion in the (110) reflection from~11.9 Å to 12.1 Å after treatment with ethylene glycol. This is the same as reported for sepiolite (Yalçin & Bozkaya,1995;Karakaya et al, 2004). A change in the d spacing of the (400) peak from 3.33Å (air-dry) to 3.42Å (ethylene glycol), is similar to the behaviour observed for sepiolite by Van de Heuvel (in Thorez, 1975).…”

A microscopic approach to the pedogenic formation of palygorskite associated with Quaternary calcretes of the Adana area, southern Turkey

“…The degradation of the Fe-bearing montmorillonite rather than saponitic smectite most likely caused the increase in the Al+Fe/Mg ratio, leading to precipitation of palygorskite in a pedogenic environment (formation within soil horizons) rather than sepiolite, which is more typically associated with precipitation from alkali-saline solutions in arid environments. This is also consistent with the fact that neither precipitation of sepiolite nor dolomitisation of calcite has occurred in these sediments (Akbulut and Kadir, 2003;Karakaya et al, 2004Karakaya et al, , 2011. The absence of palygorskite in the hardpan calcretes may be explained by the prevailing relatively more humid climatic conditions preventing the formation of palygorskite in this horizon prior to desiccation.…”

Hydrothermal macroscopic Fe-sepiolite from Oujda Mounts (Middle Atlas, Eastern Morocco)

“…The spotted areas correspond to EDAX or whole rock sepiolite analyses published in Carretero (1999), Torres Ruiz et al (1994) and López Galindo et al (1996). The striped area correspond to whole rock sepiolite analyses published in Bozkaya (1995, 2004) and Karakaya et al (2004). Igneous and sedimentary represent the microprobe sepiolite analyses published by López Galindo et al, 1996.…”