Abstract
A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v.-visible spectroscopy in the elucidation of structural, physical, and chemical properties of such systems. Spectra, which were obtained in the suspension, film, and single crystal states (where applicable), are interpreted in terms of iron-associated transitions. Microcrystalline clay minerals typically show Fe(lll) in octahedral oxo-ligand geometry whereas mica-type minerals may show a range of iron species, including octahedral Fe(III), tetrahedral Fe(III), and octahedral Fe(II). Iron affects the local site geometry and in “high iron” minerals may dictate layer geometry and subsequently the crystalline form.
Résumé
Un tour d’horizon préliminaire des spectres d’absorption électronique des minéraux argileux révèle l’utilité de la spectroscopic ultraviolet-visible si l’on veut élucider les propriétés structurales, physiques et chimiques de tels systèmes. Les spectres, obtenus avec des suspensions, des films ou des monocristaux (quand c’est possible) sont interprétés en terme de transitions associées au fer. Les minéraux argileux microcristallins montrent d’une façon typique le Fe (III) dans une géométrie octa-édrique d’oxo-ligands, tandis que les minéraux du type mica peuvent montrer toute une série d’espèces du fer, comprenant Fe (III) octaédrique, Fe III tétraédrique et Fe (II) octaédrique. Le fer affecte la géométrie locale du site et dans les minéraux “riches en fer” peut imposer une géométrie au feuillet et par là, imposer la forme cristalline.
Kurzreferat
Eine Voranalyse der elektronischen Absorptionsspektren von Tonmineralien erweist den Wert ultraviolett-sichtbarer Spektroskopie für die Erforschung der strukturellen, physischen und chemischen Eigenschaften derartiger Systeme. Spektren, die in den Suspensions-, Film- und Einkristallzuständen (je nach Verfügbarkeit) erzielt wurden, werden als Übergangsphasen in Verbindung mit Eisen interpretiert. Mikrokristalline Tonmineralien weisen typisch Fe(III) in oktahedralem Oxoverband auf, während glimmerartige Mineralien eine Reihe von Eisenarten wie oktahedralem Fe(III), tetrahedralem Fe(III) und oktahedralem Fe(II) enthalten mögen. Eisen übt auf die lokale Lagerstättengeometrie einen Einfluß aus und kann in eisenreichen Mineralien für die Schichtengeometrie und daher die Kristallform entscheidend sein.
Резюме
Предварительное исследование спектра электронного поглощения глинистых минералов выявило ценность видимой ультрафиолетовой спектроскопии в разъяснении структурных физических и химических особенностей таких систем. Спектры полученные от суспензии, на пленке и на сростке отдельных кристаллов (где относится) расшифровывались как соединения с железом. Микрокристаллические глинистые минералы обычно включают Fe(III) в восьмигранной оксо-лигиндной конфигурации, в то время как слюдистые минералы могут состоять из ряда железистых групп, включая октаэдральный Fe(III) тетраэдральный Fe(III) и октаэдральный Fe(II). Железо влияет на конфигурацию места заложения и в минералах с высоким содержанием железа оно может влиять на конфигурацию слоев и на форму кристаллов.
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Karickhoff, S.W., Bailey, G.W. Optical Absorption Spectra of Clay Minerals. Clays Clay Miner. 21, 59–70 (1973). https://doi.org/10.1346/CCMN.1973.0210109
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DOI: https://doi.org/10.1346/CCMN.1973.0210109