Solid-state nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, and X-ray powder diffraction data on the tubular, hydrous aluminosilicate imogolite were found to be fully consistent with a previously proposed crystal structure consisting of a rolled-up, 6-coordinate Al-O(OH) sheet, bonded to isolated orthosilicate groups. The calculated 29Si chemical shift of this structure agreed with the observed shift within 3 ppm. Thermal dehydroxylation of the Al-O(OH) sheet produced predominantly NMR-transparent 5-coordinate Al, but a few 4- and 6-coordinate sites and some residual hydroxyl groups may also have formed, as shown by NMR spectroscopy. Changes in the 29Si NMR spectrum on dehydroxylation suggest a condensation of the orthosilicate groups, but steric considerations rule out bonding between adjacent silicons. To account for these observations, an alternative mechanism to orthosilicate condensation has been proposed, involving the fracture and unrolling of the tubes, followed by the condensation of fragments to form a layer structure. The layer structure has a calculated 29Si chemical shift of -95.6 ppm, in good agreement with the observed value of -93 ppm.

The mechanisms by which coatings develop on weathered grain surfaces, and their potential impact on rates of fluid-mineral interaction, have been investigated by examining feldspars from a 1.1 ky old soil in the Glen Feshie chronosequence, Scottish highlands. Using the focused ion beam technique, electron-transparent foils for characterization by transmission electron microscopy were cut from selected parts of grain surfaces. Some parts were bare whereas others had accumulations, a few micrometres thick, of weathering products, often mixed with mineral and microbial debris. Feldspar exposed at bare grain surfaces is crystalline throughout and so there is no evidence for the presence of the amorphous ‘leached layers’ that typically form in acid-dissolution experiments and have been described from some natural weathering contexts. The weathering products comprise sub-urn thick crystallites of an Fe-K aluminosilicate, probably smectite, that have grown within an amorphous and probably organic-rich matrix. There is also evidence for crystallization of clays having been mediated by fungal hyphae. Coatings formed within Glen Feshie soils after ∼1.1 ky are insufficiently continuous or impermeable to slow rates of fluid-feldspar reactions, but provide valuable insights into the complex weathering microenvironments on debris and microbe-covered mineral surfaces.

We report results of high temperature photoluminescence and photoluminescence excitation studies of Er doped GaN. Er was doped into GaN either by ion-implantation or during growth by metalorganic molecular beam epitaxy (MOMBE). Using above gap excitation (λex=325nm), GaN:Er showed strong 1.54 μm Er3+ luminescence up to 550K which indicates the potential of this material for high temperature opto-electronic applications. In addition, we performed timeresolved photoluminescence excitation (PLE) measurements over the wavelength range 420 to 680 nm using a Nd:YAG pumped Optical Parametric Oscillator (OPO). Similar to our previous PLE results of Er doped AIN, we observed that Er3+ ions in GaN can be excited either through resonant pumping of Er3+ energy levels or through energy-transfer processes involving defect states. The relative contribution of direct and indirect Er3+ excitation, however, seems to depend on the material preparation method.

Measurements from powder diffraction patterns recorded at temperatures up to 950° C for the supposed equilibrium forms of albite synthesized at 800°, 900°, and 1000° C by MacKenzie (1957) indicate that only the form synthesized at 1000° C becomes monoclinic. Single-crystal measurements on heated pure natural albite (Ab99·26) show that it becomes truly monoclinic, both in geometry and intensity distribution, at 930° C, the same temperature as for the highest-temperature synthetic form. These experiments were carried out in conditions that exclude possible contamination by potassium.

Lokamanya Tilak (1856–1920) represents the full tide of ideological activity in the Indian Nationalist movement. Long overshadowed by his younger contemporary, Gandhi, his life and thought are only now, a third of a century after his death, receiving due recognition.

Prior to his entrance upon the political stage, Indian leadership afforded the spectacle of a rather polite debating society which accepted British ideals and values as almost axiomatic. Protests against government policies consisted of thoughtfully worded petitions calculated to appeal to the sense of reason and fair play of officials. Tilak saw little profit in such method, but his rivals in the Nationalist leadership, particularly G. K. Gokhale, were wedded to the traditions of British parliamentary procedure.