Abstract
Ball clay deposits in the SE of the Iberian Range (NE Iberian Peninsula) consist of Albian clays and siltstones with greyish and blackish colors, interbedded with subbituminous coals. The ball clays are nowadays mined for the manufacture of white color ceramics. The mineralogy of these deposits consists mainly of kaolinite, illitic phases, and quartz. The euhedral to sub-euhedral morphology of the kaolinites suggests their in-situ origin. The anhedral morphology of the illites and the presence of frayed illites suggest a detrital origin. At the micro-scale, authigenic kaolinite booklets are observed filling pores and forming mica/kaolinite intergrowths, in which the kaolinite grows between the cleavage sheets of pre-existing detrital mica. At nanometer scale, illite/smectite (IS) phases are detected forming interlayers with mica and kaolinite, and evidence of the replacement of mica by kaolinite is observed. The matrix consists of defective illite and kaolinite, and random mixed layers of kaolinite-I/S (Kln-IS), illite-I/S (Ilt-IS), and I/S-smectite (IS-S). The textures of illite and the presence of different types of mixed layers suggest that the expandable phases and kaolinite are products of mica alteration. The effectivity of the alteration was probably a consequence of the low pH that occurred in the environment due to the presence of abundant organic- and acidic- rich fluids.
Highlights
Plastic ball clays are commonly composed of kaolinite (25%–80%), illite and mica (10%–30%), and fine-grained quartz, and sometimes illite/smectite (IS) mixed-layered minerals occur
Several studies of the composition and ceramic properties of ball clays have been published [6,7,8,9,10,11], we found a lack of research characterizing the micro- and nanotexture of these types of clays
This study focuses on the Albian kaolinite-rich clay deposits associated with coal deposits located in the Southern Iberian Range (NE Spain), which can be considered ball clays in the sense of Wilson, 1998 [1]
Summary
Plastic ball clays are commonly composed of kaolinite (25%–80%), illite and mica (10%–30%), and fine-grained quartz, and sometimes illite/smectite (IS) mixed-layered minerals occur. Organic matter—up to 4%—is typical in these clays and a low content of coloring oxides (Fe2 O3 and TiO2 ) is a common feature. Each of these components have a specific function in the technological process [1]). The ceramic properties of plastic ball clays depend on the content of the clay minerals and on the crystallinity of the kaolinite and illite. These features influence the grain size distribution and the specific Brunauer–Emmett–Teller (BET) surface area of the clays
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