Original paper
Spanish palygorskites: geological setting, mineralogical, textural and crystal-chemical characterization
Suárez, Mercedes; García-Rivas, Javier; Sánchez-Migallón, Juan Morales; García-Romero, Emilia
European Journal of Mineralogy Volume 30 Number 4 (2018), p. 733 - 746
published: Oct 31, 2018
published online: May 4, 2018
manuscript accepted: Feb 20, 2018
final revised version received: Apr 17, 2017
manuscript received: Jan 30, 2017
DOI: 10.1127/ejm/2018/0030-2753
Open Access (paper may be downloaded free of charge)
Abstract
A representative group of palygorskites from the six most important Spanish deposits and six other occurrences were studied comparing their mineralogy, textural features, crystal-chemistry, and surface properties. These palygorskites have different geological origin: (1) sedimentary in large Tertiary continental basins, (2) hydrothermally altered volcanic rocks in the southern Spanish Peninsula, also Tertiary in age; and (3) fault-hosted pure palygorskites. The most common impurities are quartz and carbonates, both calcite and dolomite, but also feldspar, illite, smectite, and sepiolite have been identified. The structural formulae obtained show great variability between samples, as well as with respect to the theoretical formula for palygorskite, as they range from magnesian to aluminous palygorskites. The most common fibre length ranges between 1 and 10 µm but the palygorskites of hydrothermal origin are much longer, with lengths over 10 µm. The shorter fibres give rise to tightened textures, while longer fibres usually generate more open textures. These properties, along with the degree of compaction, condition the porosity of the sample, which in turn influences its surface properties. The specific surface areas obtained range between 30 m2 g−1 and 263 m2 g−1, depending on the impurities content and on the texture and crystal-chemistry; the highest values correspond to Mg-rich palygorskite.
Keywords
palygorskite • hydrothermal palygorskite • clay minerals • Tertiary Spanish basins • mineral assemblage • structural formula • texture • surface properties • SEM • adsorption of N2