Compositional Variation in Component Layers in Natural Illite/Smectite
Published chemical data for suites of mixed-layer minerals from diagenetic sedimentary rocks, hydrothermally altered tufts, and a metasomatic bentonite bed indicate that the layer charge and composition of the different components of illite/smectite (I/S) differ from one geological environment to another. It appears that the composition of the elemental smectite and illite layers in the I/S is more or less constant for samples within each geologic setting. In the examples considered, the smectite layers are predominantly montmorillonitic in character (i.e., the charge is in the octahedral site), whereas the illite layers show different types of charge sites, depending upon the suite studied. Illite layers appear to have about the same charge in all three suites studied, slightly more than 0.7 per O10(OH)2 unit, whereas the smectite layers in the different suites range in charge from about 0.3 to 0.7 per O10(OH)2 unit. Cation-exchange capacities reflect these differences in charge, although not ideally. The differences in the composition of the component layers in each geologic suite of mixed-layer clays are probably due either to differences in the bulk chemistry of the rocks in the different suites or to differences in intensive variables, such as temperature and pressure, of the regime under which they have formed.
Alkylammonium ion treatment of clay minerals in ultrathin section : A new method for HRTEM examination of expandable layers
Intercalation of n-alkylammonium ions in the interlayers of clay minerals in ultrathin sections after section preparation permits a rapid estimation of the interlayer charge of clay mineral particles using HRTEM. The layer structures of illite, vermiculite, and smectite were studied on the same section before and after n-alkylammonium treatment within a period of 34 h. The difference between smectite (13-A hyer spacing) and vermiculite layers (17-A hyer spacing) is clearly observed.
Struggles for Visibility
This article addresses the ways in which terrorists are rendered visible in the news media. By studying images used in coverage of terrorists, the article focuses on the visual construction of this figure, which symbolizes the public’s notion of the “enemy”, in terms of specific attacks and the general threat thereof as well as terrorist actors, networks, and ideologies. The article takes its point of departure in the assumption that two visual forms are prevalent for representing terrorists in the news media, “surveillance representations” and “self-representations”. Based on this assumption, the article is guided by a principal research question, namely: How are terrorists made visible in the news media through surveillance representations and self-representations and what are the prevalent genres for visually representing terrorist actors? The article draws on a theoretical framework concerning the news media’s propensity to personalize the terrorist and the mediated visibility of terrorists. Empirically, the article is based on a quantitative content analysis of coverage of terrorism by Danish public service broadcasters DR and TV2 in 2016 to provide an overview of the proportions between surveillance representations and self-representations and develop a typology of the most widespread genres: ID photography, surveillance footage, selfies and similar, and private snapshots.