1,721,101 research outputs found
Studio cristallochimico e comportamento termico di solfati naturali eptaidrati: I - Indagine su alcuni termini della serie della melanterite
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ORIGIN OF CLAY-MINERALS IN THE BONARELLI HORIZON (UMBRIAN APENNINES, CENTRAL ITALY)
No full textChemical, thermal, X-ray and statistical analyses were carried out on the clay fraction of the Bonarelli Horizon (Umbrian region, Central Italy) in order to investigate its origin. The vertical lithological sequence (organic carbon, siliceous and clay layers of varying colour and thickness) seems to change regularly, allowing the horizon to be subdivided into five sub-horizons (A to E). Sub-horizon B is clearly distinguishable from the others on the basis of the clay fractions. The presence of organic material and authigenic sulphates, constant chemical composition within a single sub-horizon, and regular repetition of the layers, show that the Bonarelli Horizon is the result of an alternation of anoxic events in a continental margin facies. A substantial contribution of volcanoclastic material is suggested for sub-horizon B
Crystal chemistry of corrensite: a review
No full textStatistical analyses of chemical data from the literature of corrensite minerals suggest a large compositional variability, more evident in octahedral than in tetrahedral coordination. Mg occupies 40- 80% of the octahedral sites, with A1 and Fe 2+ making up the remainder. Approximately 15-30% of the tetrahedral sites are filled by A1. Despite this compositional variability, distinct fields for the several types of mixed-layer trioctahedral chlorite/trioctahedral swelling layer are not apparent. Statistical analyses of the composition of corrensite compared with saponite, vermiculite, and chlorite suggest that corrensite is an intermediate between trioctahedral chlorite and trioctahedral smectite. If Fe/(Fe + Mg) > 50%, chlorite alone is favored, but with increasing Mg, chlorite appears to transform into corrensite and then, by iron oxidation, into trioctahedral smectite. Despite the chemical variability between corrensite, chlorite, and saponite, corrensite appears chemically to be a well-defined species. On the other hand, corrensite cannot be characterized chemically on the basis of its swelling component. Thus, the current definition of corrensite as a regular 1:1 interstratification of trioctahedral chlorite and either trioctahedral smectite or vermiculite is appropriate
Studio cristallochimico e comportamento termico di solfati naturali eptaidrati: II - Indagine su alcuni termini della serie dell'epsomite
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"Corrensite-like minerals" in the Taro and Ceno Valleys, Italy
No full textMineralogical properties (XRD, DTG) and chemical compositions of some chlorite-smectite interlayer minerals in alteration products of ophiolitic rocks from the Northern Apennines are presented and discussed. The presence of iron hydroxides and the continuous variation in A1203 content suggest that the corrensites are intermediate stages in the process of alteration of chlorite to smectite in an environment characterized by high element mobility. A thermal test to characterize the swelling component of the interlayer species is proposed
Vermiculite and its relation to parent materials as revealed by chemical features
No full textMineral chem. formulas, reported in the literature and calcd. from results of chem. analyses were treated by Q-mode factor anal. to examine the compositional variability of vermiculite [1318-00-9] and its parent micas. The 3 factors accounting principally the compositional variability were (1) Mg, (2) Al + Fe3+, and (3) Fe2+ + Mn + Ti. The solid soln. ranges of the dioctahedral (fine) and trioctahedral (coarse) vermiculites, biotites, hydromicas, and phlogopites were indicated by plotting their compns. in a triangle with the vertices represented by the 3 principal factors. Although the 2 types of vermiculites can be distinguished on the triangle, they show a continuous compositional range from 1 type to the other. This probably reflects the chem. rearrangement of the vermiculite following its formation from mica. Close chem. analogy is shown of vermiculite with phlogopite but not with biotite
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