Relations of Composition to Structure of Dioctahedral 2:1 Clay Minerals

Weaver, Charles E.

doi:10.1346/ccmn.1968.0160107

Cited by 8 publications

(2 citation statements)

References 8 publications

(11 reference statements)

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“…Elemental analyses obtained by microprobe are given in Table 2. Based on analytical data of Weaver and Pollard (1973), Weaver (1968), and Grim (1968, the smectite can be classified dioctahedral (with a choice of either montmorillonite or nontronite). In addition, XRD data (i.e., the 060 reflection at 1.49 A) confirm that the clay is dioctahedral.…”

Section: Clay Mineralogy and Chemistrymentioning

confidence: 99%

Smectite-Rich Pisolites of the Andersonville, Georgia, Area

Manker

Cofer

1980

Clays and clay miner.

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Section: Clay Mineralogy and Chemistrymentioning

confidence: 99%

Smectite-Rich Pisolites of the Andersonville, Georgia, Area

Manker

Cofer

1980

Clays and clay miner.

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“…General. WEAVER (1968) reviewed the variations in chemical composition of clay minerals of the 2/1 structure. The present author has assembled the literature data on 85 sufficiently pure samples of illites from sedimentary rocks.…”

Section: Mite Chemistrymentioning

confidence: 99%

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

Segonzac¹

1970

Sedimentology

338

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Summary The results obtained by the author in the study of clay‐minerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates. Kaolinite minerals are related to the surficial zones of the earth's crust where they are formed. They are characterized by the hexacoordination of aluminium. They furnish paleogeographic indications in ancient sediments. During diagenesis they are very sensitive to the geochemical environment, stable in acid conditions, unstable in alkaline conditions. However, the increase in temperature by burial causes their destruction sooner or later. In the transitional zone to metamorphism (anchizone), kaolinite is not present. Only dickite and nacrite can be observed, provided that the environment is acid. Montmorillonites are hydrated minerals. The rise in temperature and above all in pressure during burial expels water from the interlayers. Concentrated interstitial solutions of diagenesis provide cations which replace molecules of water between the layers. It is an irreversible reaction which produces 14‐Å minerals (chlorites) or 10‐Å minerals (illites), passing generally through mixed‐layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial. Mixed‐layers are intermediate stages which occur during degradation by weathering and during aggradation by deep diagenesis. This aggradation is the result of an incorporation of certain cations taken up from interstitial solutions, and of a rearrangement within the lattice. There are two major pathways: a potassium and sodium pathway, which produces the illites, then the micas, passing possibly by regular mixed‐layering of the allevardite‐rectorite type; and a magnesium pathway, which produces the chlorites, passing possibly by a regular mixed‐layering of the corrensite type. These mixed‐layers can remain stable until the border of meta‐morphism (anchizone). Micaceous clay minerals or illites form a very heterogenous group in the sediments which have been hardly diagenetized. Particles of diverse origin are found. They become more regular during burial. In deep diagenesis and the anchizone, crystallo‐graphic parameters of the illite are sufficiently well defined to serve as a scale of recrystallization, a zoneographic index. The morphology of the particles changes. Polymorphic types 1Md and 1M are replaced by the 2M‐type. The sharpness of the 10‐Å peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5‐Å and 10‐Å peaks, which is related to the chemical composition of the octahedral layer. Micas in low‐grade metamorphism, called sericites by petrographers, replace the illites discussed above. They are different from the true micas by a weaker layer charge, less than 0.9 by half‐cell. They often contain sodium (paragonitic muscovites and paragonites). The octahedral charge (zero for the muscovite) is generally high, due to the replacement of...

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Factors Limiting the Use of Standard Minerals in the X-Ray Diffraction Analysis of Clays

Douglas¹

1974

Advances in X-Ray Analysis

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Relations of Composition to Structure of Dioctahedral 2:1 Clay Minerals

Cited by 8 publications

References 8 publications

Smectite-Rich Pisolites of the Andersonville, Georgia, Area

Smectite-Rich Pisolites of the Andersonville, Georgia, Area

The Transformation of Clay Minerals During Diagenesis and Low‐grade Metamorphism: A Review

Factors Limiting the Use of Standard Minerals in the X-Ray Diffraction Analysis of Clays

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