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Articles 211 - 215 of 215
Full-Text Articles in Geology
Magic Gems, Minerals, And Fossils, Mary Margaret Murphy, H. Allen Curran
Magic Gems, Minerals, And Fossils, Mary Margaret Murphy, H. Allen Curran
Geosciences: Faculty Publications
No abstract provided.
Chemical Components And Diffusion, John B. Brady
Chemical Components And Diffusion, John B. Brady
Geosciences: Faculty Publications
Chemical components for use in the description of a system involved in a diffusion process may be selected according to the same criteria followed in the selection of components for an equilibrium system. The various possible sets of components are not independent and may be interrelated through a component transformation. Actual components are preferred over nonvariable components, since they simplify descriptions and avoid theoretically nonmeasureable quantities. Two systems involved in an interdiffusion process may always be described using components that are actual components of both systems. For example, ternary reciprocal exchange of alkalis be tween alkali feldspars and dioctahedral alkali …
Reference Frames And Diffusion Coefficients, John B. Brady
Reference Frames And Diffusion Coefficients, John B. Brady
Geosciences: Faculty Publications
No abstract provided.
Problems In Interpreting Unusually Large Burrows, Richard G. Bromley, H. Allen Curran, Robert W. Frey, Raymond C. Gutschick, Lee J. Suttner
Problems In Interpreting Unusually Large Burrows, Richard G. Bromley, H. Allen Curran, Robert W. Frey, Raymond C. Gutschick, Lee J. Suttner
Geosciences: Faculty Publications
Although marine burrows of unusually large dimensions have long been known in certain areas, they are probably much more widespread in the rock record than is generally recognized. Such burrows constitute a heterogeneous group, having little in common other than "exceptional" size. Yet their size alone unites them in difficulty of interpretation: e.g., densely spaced-dwelling burrows of combined dwelling-escape burrows as much as 12 cm in diameter and 5 m long; vertical dwelling burrows only 0.5 cm in diameter but up to 9 m long; possible escape structures as much as 24 cm in diameter and 3 m long, subsequently …
Coexisting Actinolite And Hornblende From West-Central New Hampshire, John B. Brady
Coexisting Actinolite And Hornblende From West-Central New Hampshire, John B. Brady
Geosciences: Faculty Publications
The coexistence of actinolite and hornblende and of cummingtonite and hornblende has been observed in garnet-zone and staurolite-kyanite-zone amphibolites of the Ammonoosuc Volcanics near Hanover, New Hampshire. The amphibole pairs occur both as separate grains and as intergrowths with boundaries that are optically and chemically sharp, but geometrically irregular; no exsolution lamellae were observed.Electron microprobe analyses of the amphibole pairs show that: (1) hornblende is richer in Al, Na, K, Ti, and Fea+,and has a lower Mg/(Me f Fe) ratio than the coexisting actinolite; (2) hornblende is enriched in Al, Na, and Ca, but has a similar Mel(Mg f Fe) …